Method for treating tension-type headache with inhibitors of nitric oxide and nitric oxide synthase

ABSTRACT

Tension-type headache is treated by interacting with neuronal transmission in relation to pain in connection with headache in a way which prevents or decreases sensitization of second order nociceptive neurons. In particular, treatment is performed by administration of an effective amount of a substance which prevents or decreases central sensitization. Important examples of such substances are substances which interact with nitric oxide, such as nitric oxide synthase (NOS) inhibitors, such as L-NMMA or L-NAME or L-NIO or L-NNA. According to a broader aspect of the invention tension-type headache is treated by administration of substances which are effective in preventing or decreasing pain in connection with tension-type headache, such as the substances mentioned above. Accordingly, the invention relates to treatment of tension-type headache by administration of substances which substantially inhibit the activity of nitric oxide synthase (NOS), such as NOS inhibitors, such as L-NMMA or L-NAME or L-NIO or L-NNA.

This application is a nonprovisional claiming the benefit under 35 USC §119(e) of provisional Ser. No. 60/085,413, filed May 14, 1998. Thisapplication is also a continuation-in-part of PCT/DK97/00502, filed Nov.4, 1997, a PCT application designating the United States, which is anonprovisional claiming the benefit under 35 USC § 119(e) of provisionalSer. No. 60/030,294, filed Nov. 5, 1996. All of the above applicationsare hereby incorporated by reference in their entirety.

FIELD OF THE INVENTION

The present invention relates to a method of treatment or prevention oftension-type headache in a human in need of such treatment. Inparticular, the invention relates to a method of treatment oftension-type headache comprising the administration of an agent oragents effective for the prevention or reduction of centralsensitization

GENERAL BACKGROUND

Types of Clearly Defined Headache Disorders.

Previously, headache disorders were not clearly distinguished and it waswidely believed that they formed part of a continuum and were stronglyrelated. In 1988, The International Headache Society, (IHS) via its adhoc committee on classification published a document entitledClassification and Diagnostic Criteria for Headache Disorders, CranialNeuralgias and Facial Pain (Classification and Diagnostic Criteria forHeadache Disorders, 1988). A new entity was here defined by name oftension-type headache. This entity was practically the same asconditions previously called tension headache, muscle contractionheadache, psycho-myogenic headache and idiopathic headache. The IHSclassification also defined a number of other specific headachediseases. Today it therefore gives no meaning to talk about headache ingeneral. It would be the same as to discuss bellyache and chest painwithout specifying its type and etiology. Due to the development indiagnostic accuracy research results obtained before 1988 have uncertainvalidity.

Tension-type headache was subdivided by the IHS Classification Committeeinto an episodic form occurring less than half of all days and a chronicform occurring half of all days or more. Furthermore, both of thesedivisions were further subdivided into a form with disorder ofpericranial muscle and a form without such disorder. It is thus crucialthat research and patents specify which of the subforms are included.

Before the entity of tension-type headache was created, it was widelybelieved that this kind of headache was caused by muscle ischemia, aconcept later disproven by the present inventors nark et al. 1990) Theterm tension-type headache was created in order to indicate that expertsdisagreed with the notion of tension-type headache being simply a kindof muscle pain. In fact, the term idiopathic headache was suggested.There is only a moderate co-morbidity with neck pain and low back painin sufferers of tension-type headache. Furthermore, Electromyography(EMG)-measurements have failed to detect an increase of musclecontraction sufficient to cause pain on a purely mechanical basis intension-type headache patients whereas central factors such asdepression and anxiety have been attributed a significant role. Finally,a genetic factor has recently been shown to be involved in tension-typeheadache (Østergaard et al. 1996). From the point of view of mechanismsand definition tension-type headache is thus a specific entity which mayor may not share mechanisms with muscle pain in the head and in otherparts of the body. The classification and diagnostic criteria fortension-type headache are shown in Tables I and II.

TABLE I Classification of headache disorders, cranial neuralgias, andfacial pain (Headache Classification Committee 1988).  1. Migraine  2.Tension-type headache  3. Cluster headache and chronic paroxysmalhemicrania  4. Miscellaneous headaches unassociated with structurallesion  5. Headache associated with head trauma  6. Headache associatedwith vascular disorders  7. Headache associated with non-vascularintra-cranial disorder  8. Headache associated with substances or theirwithdrawal  9. Headache associated with noncephalic infection 10.Headache associated with metabolic disorder 11. Headache or facial painassociated with disorder of cranium,   neck, eyes, nose, sinuses, teeth,mouth or other   facial or cranial structures 12. Cranial neuralgias,nerve trunk pain and deafferentation pain 13. Headache not classifiable

TABLE II Diagnostic criteria for episodic and chronic tension-typeheadache (Headache Classification Committee 1988) II.1. Episodictension-type headache A. At least 10 previous headache episodesfulfilling criteria B-D listed below. Number of days with such headache<180/year (<15/month) B. Headache lasting from 30 minutes to 7 days C.At least 2 of the following pain characteristics: 1. Pressing/tighteningquality 2. Mild or moderate severity (may inhibit, but does not  prohibit activities) 3. Bilateral location 4. No aggravation bywalking stairs or similar routine   physical activity D. Both of thefollowing: 1. No nausea or vomiting (anorexia may occur) 2. Photophobiaand phonophobia are absent, or one but not the   other is present E. Atleast one of the following: 1. History, physical and neurologicalexaminations do not suggest   one of the disorders listed in groups 5-112. History and/or physical and/or neurological examinations do   suggestsuch disorders, but they are ruled out by   appropriate investigations3. Such disorders are present, but tension-type headache does   notoccur for the first time in close temporal   relation to the disorderII.2. Chronic tension-type headache A. Average headache frequency 15days/month (180 days/year) for 6 months fulfilling criteria B-D listedbelow B. At least 2 of the following pain characteristics: 1.Pressing/tightening quality 2. Mild or moderate severity (may inhibit,but does not   prohibit activities) 3. Bilateral location 4. Noaggravation by walking stairs or similar routine   physical activity C.Both of the following: 1. No vomiting 2. No more than one of thefollowing:   Nausea, photophobia or phonophobia D. At least one of thefollowing: 1. History, physical and neurological examinations do not  suggest one of the disorders listed in groups 5-11 2. History and/orphysical and/or neurological examinations do   suggest such disorders,but they are ruled out by   appropriate investigations 3. Such disordersare present, but tension-type headache does   not occur for the firsttime in close temporal   relation to the disorder

Epidemiological studies done by the inventors have shown that chronictension-type headache affects three percent of the population at anygiven time, the lifetime prevalence being as high as six percent(Rasmussen et al. 1991). Severe episodic tension-type headache definedas persons having headache twice a week or more occurs in approximatelyten percent of the population. Thus, tension-type headache is a seriousproblem with significant socio-economic implications, involving enormousloss of workdays and quality of life.

Previous Findings in General Pain Physiology and Pain Pharmacology

The possible pathogenic mechanisms of tension-type headache havepreviously been studied and discussed by Langemark et al. (Langemark etal. 1987, 1988, 1989) and by the group of Jean Schoenen (Schoenen et al.1987, 1991a, b). The latter group have mainly focused onelectrophysiological recordings as electromyography, and the jaw openingreflex as reflected by the so-called exteroceptive silent period (ES2)(Schoenen et al. 1987). On the basis of shortened ES2 periods inpatients with chronic tension-type headache compared to healthy controlsa limbic dysfunction was suggested, but these results have later beendisproven by more systematic investigations (Bendtsen et al. 1996a,Lipchik et al 1996, Zwart and Sand, 1996). Schoenen and other groupshave also studied mechanical pain thresholds on the extremities as wellas in the cranial region and decreased mechanical pain thresholds inseverely affected patients with chronic tension-type headache werereported (Schoenen et al. 1991a, Langemark et al. 1989), whereaspatients with the episodic form of tension-type headache are reported tohave normal thresholds compared to healthy controls (Hatch et al. 1992,Goebel et al. 1992, Jensen et al. 1993b). These authors suggested thatcentral mechanisms may be involved in the chronic subform and that theperipheral mechanisms played a role in the episodic form, but providedno further clues or arguments about the underlying mechanisms. One morerecent congress presentation and two scientific papers by the presentinventors have focused on the sensory mechanisms in tension-typeheadache as decreased thresholds and tolerances were found in andoutside the head of patients with chronic tension-type headacheindicating a generally increased sensitivity to noxious and innocuousstimuli (Bendtsen et al. 1995b, 1996b and 1996c). Similarly a congressreport and a scientific paper present data from patients studied duringand outside a spontaneous tension-type headache episode (Jensen et al.1995a and 1995b). Muscle tenderness was increased during the headacheepisode, whereas mechanical pain thresholds remained unchanged andthermal pain tolerance decreased. It was concluded that a peripheralsensitization may be one of the primary sources of pain and that centralsensitization may contribute to and maintain the pain in chronictension-type headache. However, these data did not provide any furtherclues for more specific localizations of the sensitization, could notlead to a precise experimental model and finally did not lead toguidance for specific treatment of tension-type headache.

Peripheral Induction of Central Sensitization

One of the most exciting developments in pain research over the pastdecades has been the recognition that the response generated by thesomatosensory system to a defined input is not fixed or static. Inparticular, the increased knowledge on central sensitization, i.e.increased excitability of neurons in the central nervous system, hasbeen a major breakthrough in the understanding of chronic pain. In 1983Woolf and colleagues (Woolf 1983) demonstrated for the first time that aprolonged noxious input from the periphery is capable of sensitizingspinal dorsal horn neurons. It has later been demonstrated that thecentral sensitization is induced by repetitive C-fibre, but not A-fibre,input (Yaksh and Malmberg 1994). In the sensitized state, alow-intensity stimulus can generate pain, the phenomenon of allodynia.The low-intensity stimulus is mediated via low-threshold afferents,A-b-fibres, which do not normally mediate pain, and it has been.suggested that the major cause of increased pain sensitivity in thechronic pain condition is an abnormal response to A-b-sensory input(Woolf and Doubell 1994). The original findings by Woolf and colleagueson spinal dorsal horn sensitization have later been confirmed bynumerous independent laboratories (Mense 1993), and a similarsensitization of trigeminal brainstem nociceptive neurons followingstimulation of craniofacial muscle afferents has been reported by Hu etal. (Hu et al. 1992). While central sensitization may be of relevance inmany different chronic pain conditions it is particular likely in musclepain, because input from muscle nociceptors is more effective ininducing prolonged changes in the behavior of dorsal horn neurons thanis input from cutaneous nociceptors (Wall and Woolf 1984).

SUMMARY OF THE INVENTION

The inventors of the present invention have discovered that the centralnervous system is sensitized in patients suffering from increasedmyofascial pain in connection with tension-type headache because ofprolonged nociceptive input from myofascial tissues. The presentinventors were then able to devise, for the first time, an effectivetreatment of tension-type headache, which comprises interacting withneuronal transmission connected with nociception so as to prevent orreduce central sensitization.

A better understanding of the principle of the invention can be derivedfrom the detailed description of the scientific background in thescientific section below.

Scientific Section

Previous Findings in General Pain Physiology and Pain Pharmacology andPrevious Findings in Tension-type Headache.

Pain physiology and pain pharmacology have mostly been elucidated inanimal studies. There are, however, no animal models with any provenvalidity in tension-type headache. Furthermore, these animalexperimental studies are done in anaesthetized animals while thesensation of pain by definition can only occur in awake beings. Most ofthe experiments are also of an acute nature stimulating for millisecondsand recording responses for seconds, minutes or hours and are thereforeof uncertain validity for chronic tension-type headache. Finally, onlyfew studies have been done on myofascial tissues projecting via thetrigeminal nerve while the huge body of knowledge otherwise availabledeals with mechanisms of the spinal cord. None of the experimentalanimal studies mention any form of headache, neither do they suggestthat the results of these studies may be utilized for the treatment oftension-type headache. However, after the crucial findings leading tothe present invention were made, it is clear that the implications ofthe findings in relation to general pain physiology can also be utilizedin relation to tension-type headache.

With respect to medicinal treatment of tension-type headache, the priorart mentions a variety of substances. The substance Flupirtin (ethyl2-amino-6-(4-fluorobenylamino)-3-pyridylcarbamate), which is suggestedto work as an NMDA glutamate receptor antagonist (Schwartz et al. 1981),has been suggested for use in the treatment of chronic or episodictension-type headache, as disclosed in EP 0 659 410 A2, and according toWörz et al., 1996, it has shown positive effects. However, in thesedocuments the substance is described as a muscle relaxant, and themechanism by which it is proposed to exert its effect in the treatmentof various conditions, including tension-type headache, is by loweringmuscle tension. Thus, as opposed to the present inventors, the prior artunderstands and explains tension-type headache as a condition directlyand primarily caused by muscle tension. WO 96/32386 concernsarylglycinamide derivatives which are antagonists of neurokinins, andthese compounds are broadly claimed for use in the treatment of a widevariety of conditions in which neurokinins are supposed to beimplicated. Tension-type headache is mentioned as such a condition, butthere is no indication of what the mechanism of neurokinin involvementmight be. For all the above-mentioned prior art documents, it can besaid that the concept of central sensitization in relation totension-type headache as introduced by the present inventors, is notdescribed or contemplated at all. Indeed, the prior art does not appearto be concerned with the underlying physiological mechanisms oftension-type headache, but seems to reflect presently held notions ofpain physiology in general.

In connection with the present invention, the term “arylglycinamidederivative as disclosed in WO 96/32386” means a compound as defined inany of claims 1-17 of WO 96/32386. As appears from the claims herein,these arylglycinamide derivatives are excluded from the definitions ofall aspects of the present invention. The excluded arylglycinamidederivatives of claims 1-17 of WO 96132386 are all comprised by thedefinition given in claim 1 of WO 96132386. Thus, whenever reference ismade to an “arylglycinamide derivative as disclosed in WO 96/32386”,this means an arylglycinamide derivative covered by the definition ofclaim 1 of WO 96132386, that is:

Arylglycinamide derivatives of the general formula I

and their pharmaceutically acceptable salts, in which

Ar is unsubstituted or 1-5 times substituted phenyl, or unsubstituted or1 or 2 times substituted naphtyl [the substituents of phenyl andnaphthyl independently of each other being halogen (F, Cl, Br, J), OH,(C₁-C₄)alkyl, O—(C₁-C₄)alkyl, CF₃, OCF₃ or NR⁹R¹⁰ (wherein R⁹ and R¹⁰independently of each other are H, methyl or acetyl)], or Ar is phenylsubstituted with —OCH₂O— or —O(CH₂)₂O—;

R¹ and R² together with the N to which then are bound form a ring of theformula

wherein

p is 2 or 3,

X means oxygen, N(CH₂)_(n)R⁶ or CR⁷R⁸, wherein

n is 0, 1 or 2,

R⁶ is (C₃-C₇)cycloalkyl, phenyl or naphthyl, each phenyl optionallybeing 1-3 times substituted with halogen (F, Cl, Br, J), (C₁-C₄)alkylO—(C₁-C₄)alkyl, CF₃, OCF₃ or NR⁵R⁶ (wherein R¹⁵ and R¹⁶ independently ofeach other are H, methyl or acetyl);

R⁷ and R⁸ have one of the following meanings

a) when R³ is unsubstituted or substituted phenyl, then R⁷ and R⁸ are H,

b) when R₈ is H, —CONH₂, —NHC(O)CH₃, —N(CH₃)C(O)CH₃, CN,

or —C(O)N((C₁-C₃)alkyl)₂,

then R⁷ is phenyl, phenyl substituted with 1-3 substituents [wherein thesubstituents independently from each other are halogen (F, Cl, Br, J),(C₁-C₄)alkyl, O—(C₁-C₄)alkyl, CF₃ or OCF₃], piperidinyl,1-methylpiperidinyl,

or

c) R⁷ and R⁸ together form the moiety

R³ is H, (C₁-C₄)alkyl, unsubstituted or 1-3 times substituted phenyl,wherein the substituents independently of each other are halogen,(C₁-C₄)alkyl, O—(C₁-C₄)alkyl, CF₃, OCF₃ or NR¹⁷R¹⁸ (wherein R¹⁷ and R¹⁸independently of each other are H, methyl or acetyl);

R⁴ is phenyl(C₁-C₄)alkyl or naphthyl(C₁-C₄)alkyl wherein phenyl may besubstituted with 1-3 substituents. which substituents independently ofeach other are halogen (F, Cl, Br, J), (C₁-C₄)alkyl, O—(C₁-C₄)alkyl,CF₃, OCF₃ or NR¹⁹R²⁰ (wherein R¹⁹ and R²⁰ independently of each otherare H, methyl or ethyl,

and

R⁵ is H, (C₁-C₄)alkyl, (C₃-C₆)cycloalkyl, CH₂COOH, —CH₂C(O)NH₂, —OH orphenyl(C₁-C₄)alkyl.

Novel Experimental Evidence For Neuronal Sensitization in Tension-typeHeadache.

As discussed, previous studies in tension-type headache have in generalterms indicated that there may be sensitization of muscle andnociceptive afferents and also in a non-specific way have suggested somekind of central sensitization. Whether one or the other kind ofsensitization is the more important or whether indeed they both co-existhas not been clear. Recent series of experiments by the presentinventors have now clearly shown that tension-type headache is indeedmuch more complicated than previously anticipated; thus neither thephenomenon of peripheral sensitization nor that of unspecific centralsensitization does in isolation explain the condition. The studies ofthe present inventors have demonstrated that mechanical force due tocontraction of chewing muscles may induce peripheral sensitization inchewing muscles and that this peripheral sensitization is an importantfactor which may or may not induce headache (Jensen and Olesen 1996).Whether this happens depends on the response of the central nervoussystem Further experiments have shown for the first time that aqualitatively altered pain perception related to sensitization of secondorder nociceptive neurons is chronically present in subjects withtension-type headache (Bendtsen et al. 1996c). This is believed to befar the most important abnormality in tension-type headache. Thirdly,recent studies by the present inventors have demonstrated that inaddition to sensitization of second order nociceptive neurons, there isalso a component of a more unspecific sensitization of pain pathways athigher levels of the central nervous system (Bendtsen et al. 1996b).While sensitization of second order neurons is believed to be segmental(located only in those segments of the spinal cord/trigeminal nucleuswhich receive afferents from myofascial tissues), the sensitization ofhigher centers is of a general nature and results in increased painsensitivity all over the body. It is anticipated that the sensitizationof supraspinal neurons is a consequence of the considerably increasednociceptive input to these neurons (Lamour et al. 1983) because of thesensitization at the level of the spinal dorsal horn/trigeminal nucleus.Thus, the generalized pain hypersensitivity reflects the sensitizationof second order neurons. Moreover, a recent study (Ashina et al. 1998a,Example 4 herein) by the inventors has demonstrated that the nitricoxide synthase (NOS) inhibitor, L-N^(G) methyl arginine hydrochloride(L-NMMA), is effective in the treatment of patients with chronictension-type headache. Since NOS inhibitors reduce spinal dorsal hornsensitization induced by continues painful input from the periphery (Maoet al. 1997) this study provides additional evidence for centralsensitization at the level of the spinal dorsal horn/trigeminal nucleusin patients with tension-type headache. Another recent study (Example 8herein) by the inventors has demonstrated that L-NMMA reduces musclehardness in patients with tension-type headache. Increased musclehardness is anticipated to reflect central sensitization, since it isknown that central sensitization may increase the drive to motor neuronsboth at the supraspinal and at the segmental level (Woolf 1983),resulting in increased muscle activity and thereby in increased musclehardness. This study, therefore, also points towards centralsensitization in tension-type headache. Finally, the present inventorshave recently demonstrated that experimental tooth clenching inducesincreased tenderness of masticatory muscles in patients withtension-type headache and that the increased tenderness precedes theinduced headache by several hours (Jensen and Olesen 1996), and that thecentral nervous system is sensitized only in patients with tenderpericranial muscles and not in patients without tender pericranialmuscles (Jensen et al. 1998). Together, these studies demonstrate thatthe central nervous system is sensitized at the level of the spinaldorsal horn/trigeminal nucleus in patients with tension-type headachebecause of prolonged nociceptive input from myofascial tissues. On thebasis of the combined findings of the inventors, a novel and rathercomplex model of the mechanisms of tension-type headache has beendeveloped, as depicted in FIG. 1. In the following the model isdescribed in details and its significant implications for devisingsuccessful future drug treatment of tension-type headache are discussed.

The model is illustrated in FIG. 1, in which the abbreviations have thefollowing meaning:

V: Trigeminal nerve,

C2, C3: Second and third cervical segment of the spinal cord,

PAG: Periaquaductal grey,

DRN: Dorsal raphe nuclei,

on-ells: cells in ventromedial medulla, which activate pain pathways,for instance by reducing the threshold in the tail flick test.

C, Ad, Ab: Fibers of the C, Ad, and Ab type

Model For the Development of Tension-type Headache Involving NeuronalSensitization.

The main circuitry in FIG. 1 is the following:

Voluntary muscle activity is initiated by the supplementary motor area.This activates the motor cortex which again activates the motor nucleusof the trigeminal nerve and anterior horn cells of the C2 and C3segments of the spinal cord causing contraction of chewing and neckmuscles. Simultaneously with the activation of motor cortex, thesupplementary motor area also activates the antinociceptive system.Therefore normal muscle activity, even when vigorous, is not normallyperceived as painful. Another way of activating the motor pathways isvia the limbic system which is concerned with emotions. When this systemis activated, as in states of anxiety and stress, it is envisaged thatthe motor cortex and the pain facilitatory system are activatedsimultaneously. Thus, emotionally induced involuntary muscle contractionusually induces myofascial tenderness and pain. Both voluntary andemotionally triggered muscle contraction via mechanical stress andperhaps neurogenic inflammation increase afferent input from myofascialtissues via C-fibers, A-d-fibers and A-b-fibers. C-fiber input isresponsible for slow pain and when prolonged, causes the so-calledwind-up phenomenon in second order neurons located in the nucleus of thetrigeminal tract and in segments C2 and C3 of the dorsal horn of thespinal cord. Wind-up is associated with increased sensitivity of secondorder neurons and an increase of their receptive fields. Furthermore,input via A-b-fibers becomes painful which is called allodynia. Inputfrom the periphery in a state of wind-up causes a more intense pain thannormally. With repeated or chronic micro traumatic or inflammatoryreactions in myofascial tissues peripheral nociceptores, primarilyprojecting via C-fibers, become sensitized. Substances involved inperipheral sensitization include the potassium ion, bradykinin,histamine, ATP, neurotrophins and possibly other growth factors (Meyeret al. 1994).

Synaptic Mechanisms in the Spinal Dorsal Horn/trigeminal NucleusInvolved in Central Sensitization

How does repetitive C-fibre input to the spinal dorsal horn result inabnormal responses to normal Ab-fibre inputs, i.e. in centralsensitization? The most likely answer is that C-fibre releasedneurotransmitters increase the excitability of dorsal horn neurons, sothat previously ineffective Ab-fibre inputs to nociceptive dorsal hornneurons become effective (Woolf and Thompson 1991). Severalneurotransmitters are known to be involved in nociceptive transmissionfrom C-fibre afferents to second order neurons in the spinal dorsalhorn. These neurotransmitters can largely be divided into gases, intopeptides, which are chains of amino acids, or into excitatory orinhibitory amino acids, which are chemically single amino acids and intoexcitatory or inhibitory amines.

Gases

The freely diffusible gas nitric oxide (NO) is probably released fromC-fibres and acts after binding to the enzyme guanylate cyclase inpostsynaptic neurons. However, even though NO is considered of majorimportance in central sensitization, its exact role as aneurotransmitter is not yet clarified (Meller and Gebhart 1993).

Neurokinins

Neurokinins are a family of related peptides, including substance P,neurokinin A, neurokinin B and bradykinin which are known to be releasedfrom C-fibres. Currently there are three known subclasses of receptorsfor these peptides: neurokinin-1, (NK1) NK₂ and NK₃ receptors.

PACAP

PACAP is expressed in abundant amounts in dorsal horn neurons and isbelieved to play a significant role in pain transmission or themodulation of pain transmission.

Calcitonin Gene-related Peptide (CGRP)

The exact role of this peptide in pain transmission is not known becauseof lack of selective receptor antagonists. However, CGRP probablyprotracts the breakdown of substance P in the synaptic cleft, therebyadding to the level of excitability of the spinal cord (Dickenson 1996).

Other Peptides

Several other peptides such as somatostatin, neuropeptide Y and galaninmay be important, but their exact role in central sensitization is notyet known.

Excitatory Amino Acids

It now appears that the excitatory amino acid glutamate plays a dominantrole in the development of central sensitization. Glutamate is used bymost neurons in the brain and spinal cord as their major excitatorytransmitter. The actions of glutamate are mediated by 4 differentreceptor classes: the N-methyl-D-aspartate (NMDA), thea-amino-3-hydroxy-5-methyl-4-isoxazolyl-propionic acid (AMPA), thekainate receptors, and the metabotropic receptors. Of these receptors,especially the NMDA receptors are considered to be of crucial importancein central sensitization (Coderre et al. 1993).

Adenosine

The central terminals of primary afferent fibers do express adenosinereceptors (Levine and Taiwo 1994). Via these receptors, adenosine caninhibit voltage-gated calcium channels via activation of a G-proteinresulting in an inhibition of transmitter release from the primaryafferent neuron (Rang et al. 1994). Adenosine agonists may also act toinhibit the firing of wide-dynamic neurons, probably through an increasein potassium conductance. Furthermore, adenosine has been reported toblock the release of glutamate (Yaksh and Malmberg 1994). In support ofthese finding intrathecal adenosine has been shown to increase thenociceptive threshold (Yaksh and Malmberg 1994). Adenosine does alsoplay a role in the peripheral tissues. In the primary afferentnociceptor adenosine acting at the A₁-receptor inhibit hyperalgesia,while adenosine acting at the A₂-receptor produces hyperalgesia viaelevation of intracellular cAMP (Levine and Taiwo 1994).

Gamma Amino Butyric Acid (GABA)

GABA is an important inhibitory transmitter in the central nervoussystem, and it has been suggested that the encoding of low-thresholdmechanical stimuli as innocuous depends completely upon the presence ofa tonic activation of intrinsic glycine and/or GABAergic neurons (Yakshand Malmberg 1994). Furthermore, it has been demostrated that theadministration of GABA antagonists can produce allodynia (Woof 1994).GABA_(B) agonists may act to inhibit the firing of wide-dynamic neurons,probably through an increase in potassium conductance (Yaksh andMalmberg 1994) and GABA may also reduce the amount of transmitterrelease from the central terminals of primary afferent fibers by openingof chloride channels (Rang et al. 1994).

5-hydroxytryptamine (5-HT)

5-HT is a very important transmitter in the modulation of pain. While5-HT has both analgesic and algesic properties, it acts mainly as aninhibitory pain transmitter in the central nervous system (Roberts1992). Thus, when 5-HT is applied directly to the spinal cord, itproduces analgesia (Fields and Basbaum 1994). The antinociceptiveeffects of 5-HT are mediated via many different 5-HT receptor subtypes.Thus, it is known that both the 5-HT₁, 5-HT₂ and 5-HT₃ receptors areinvolved in antinociception (Fields and Basbaum 1994).

Norepinephrine (NE)

Like 5-HT, also norepinephrine (NE) plays an important role as anendogenous antinociceptive transmitter. In general, noradrenergiccontrols are mediated at the spinal level by the action at thea-2-adrenergic receptor (Field and Basbaum 1994). The a-2-agonistclonidine has been shown to block the release of transmitters andpeptides in primary afferent terminals by presynaptic action, and it ismost likely that the analgesic effects of the tricyclic antidepressantspartly depend on their inhibition of norepinephrine re-uptake (Boivie1994).

Intracellular Mechanisms in the Spinal Dorsal Horn/trigeminal NucleusInvolved in Central Sensitization.

Why are the NMDA receptors considered so important? The actions of manyreceptors on neuronal excitability are via opening or closing of ionchannels. The ion channel for the NMDA receptors allows vast amounts ofcalcium into the neuron, so much that the resultant increase inexcitability exceeds that produced by all other receptors (Dickenson1996). The increase in intracellular calcium initiates a cascade ofbiochemical events. Thus, calcium activates a calmodulin-sensitive siteon NO synthase, which results in the production of NO. NO may thereafteract via at least three different mechanisms: 1) it may act in the neuronwhere it is produced, e.g. by increasing cyclic guanylate monophososphate (cGMP) levels which again will activate protein kinases orby inducing the expression of immediate early genes. The protein kinasesand the protein products of immediate early genes may then act as thirdmessengers and control the expression of other genes involved in thesynthesis of growth factors, channels proteins, peptides and enzymes; 2)it may act as a retrograde transmitter by diffusion to the presynapticneuron where it modulates excitability and enhances synapticconnections; and 3) it may diffuse to adjacent neurons, e.g.interneurons (Meller and Gebhart 1993). Another important result ofincreased intracellular calcium is the activation of phospholipase A₂,leading to increases in intercellular arachidonic acid and thesubsequent formation of cyclooxygenase and lipooxygenase products.Prostaglandins have been shown to increase calcium conductance on dorsalroot ganglion cells and to increase the secretion of primary afferentpeptides such as substance P (Yaksh and Malmberg 1994). Activation ofthe NMDA receptors thus has dramatic consequences and the receptors aretherefore usually blocked, such that they do not participate in normaltransmission. This channel block, which is mediated by physiologicallevels of Mg²⁺ ions, can only be removed by sufficient repeateddepolarization of the membrane. It is suspected that the neurokininsco-released with glutamate from C-fibers contribute to the removal ofMg²⁺ ions. This important action of the neurokinins is probably mediatedvia NK₁ and NK₂ receptors (Dickenson 1996). Also the protein kinasesactivated by NO will feed back on the NMDA receptors, causingphosphorylation and partial removal of the Mg²⁺ channel blockade (Woolf1996). Other glutamate receptors are probably also involved in centralsensitization, but the exact mechanisms are not yet known.

Altered Pain Perception After Central Sensitization

The increased excitability of neurons in the spinal dorsalhorn/trigeminal nucleus has dramatic consequences for the painperception in the individual patient. In the sensitized state, pain canbe generated by low-threshold Ab-fibers (allodynia) (Torebjörk et al.1992), the response to activation of high-threshold afferents isexaggerated (hyperalgesia) (Woolf 1994), and since the receptive fieldof the dorsal horn neuron is increased, the central sensitization willalso be manifest as a spread of hypersensitivity to uninjured sites(secondary hyperalgesia) (Torebjöork et al. 1992).

Central Sensitization in the Brain

When noxious input is received in the nucleus of the trigeminal tract,its further transmission to the thalamus and sensory cortex depends onthe intensity of the input and on the balance between pain inhibitingand pain facilitating descending systems originating from the brainstem. When the pain inhibiting system is activated, it decreases thelikelihood that incoming stimuli are being transmitted to the thalamusand, alternatively, when the facilitatory system is activated, itincreases the likelihood of this event. From the thalamus, nociceptionis projected further to the sensory cortex. Via unknown mechanisms paincauses a reflex increase in muscle tone. It is envisaged that thisresponse to pain is mediated via the limbic system because pain andanxiety are closely interrelated. There is also a cross-talk betweennociception and motor activity at the level of the trigeminalnucleus/spinal cord. Finally, pain activates the sympathetic systemcausing release of noradrenaline. This again is responsible for anincreased pain sensation, so-called sympathetically aggravated ormaintained pain.

Detailed Model for the Progression of Tension-Type Headache

The progression of episodic tension-hype headache into chronictension-type headache often takes several years and happens only in aminority of episodic tension-tape headache sufferers. A geneticdisposition (Østergaard et al. 1996) as well as several environmentalfactors seem to be involved in the development of chronicity. Despitethe fact that the progression is continuous, it is best illustrated by anumber of scenarios.

Scenario 1:

Mild and moderate muscle contraction in normals. Voluntary musclecontraction in relation to normal functions such as cheating or headholding is initiated from the supplementary motor cortex. This isprobably associated with only a minor increase in nociception frommyofascial tissues and no wind-up in non-headache sufferers.Simultaneously the antinociceptive system is activated such that nosensation of pain occurs.

Scenario 2:

Forceful and/or long-lasting muscle activity in normals. Withparticularly vigorous muscle activity and especially when it is veryprotracted, the strain on myofascial tissues may be such thatnociception is rather marked and tenderness and local pain may occur,but it is rapidly controlled by local reparative mechanisms inmyofascial tissues and a continuously active antinociceptive system.Tenderness without spontaneous pain on the day after exercise may be aresult of this balance or may be a purely local phenomenon.

Scenario 3:

Involuntary muscle activity induced by the limbic system in normals. Incontrast to activation initiated by the supplementary motor area, musclecontraction initiated by the limbic system is not associated with anincreased antinociceptive activity On the contrary it is proposed to beassociated with increased activity in the pain facilitatory system. Analternative is a decrease in the activity of the antinociceptive system,but this is unlikely because this system is normally not tonicallyactive. Limbic initiated muscle activity therefore causes pain even withmoderate degrees of contraction and also with relatively short-lastingcontractions. However, in normals the drive from the limbic system isshort lasting and so are the mild changes in myofascial tissues inducedby the motor activity. The headache is therefore self limiting.

Scenario 4:

Voluntary contraction in patients with severe episodic- and chronic butnot daily tension-type headache. In most of these individuals voluntarymuscle activity will be painful. In part this is due to permanentsensitization of second order neurons in the nucleus of the trigeminaltract, in part it is due to the fact (Jensen and Olesen 1996) that theantinociceptive system is not activated as normally. Contractiontherefore aggravates tenderness and causes pain from the myofascialstructures (Jensen and Olesen 1996) The process of reverting the systemback to normal may be more or less effective. This variable duration ofthe initiating stimulus accounts for the variable duration of theheadache.

Scenario 5:

Severe (daily) chronic tension-type headache.

In severe chronic tension-type headache there is a state of chronicsensitization in myofascial tissues and in central pain pathways both atthe second order neurons and at higher centers. There is a minorconstant elevation of EMG signal from cranial muscles. In addition, themost severe cases also have a more diffuse sensitization revealed indecreased pain thresholds throughout the body (Bendtsen et al. 1996b).Chronically increased muscle activity maintains a state of chronicperipheral sensitization which again maintains a state of chronicsensitization in the second order neurons in the nucleus of thetrigeminal tract (Bendtsen et al. 1996c). This causes steady inflow ofnociceptive signals to the thalamus and the perception of chronic painby the sensory cortex. This again activates the limbic system andstimulates tonic involuntary muscle activity. In this situation ofchronic pain there is probably also activation of the sympatheticnervous system adding a component of sympathetically mediated pain tothe whole picture. On top of this chronic situation of sustained pain,it is easy to see how additional strain would result in increased andprolonged pain. A further increase in muscle activity would for instancein the sensitized peripheral myofascial tissues lead to a stronger thannormal nociceptive input to the already sensitized nucleus of thetrigeminal tract which would project to already sensitized hemisphericpain centers. A vicious circle has been set up and it may becomepermanent due to changes in gene transcription and consequent structuralchanges in neurons and synapses.

Rationale For the Novel Strategy According to the Invention For theTreatment of Tension-type Headache

Previous treatments have primarily been directed towards reducing musclecontraction i.e. biofeedback treatment, physiotherapy, dental treatment,exercises and muscle relaxants. All of these treatments have had limitedor no success. It follows from the model according to the presentinventors that therapeutic intervention should be directed primarilytowards the afferent system and above all against sensitization ofsecond order neurons in the nucleus of the trigeminal tract and uppercervical segments. Furthermore, it follows that while intervention usingperipherally acting analgesics or other measures which reduce peripheralnociceptive input is sufficient in episodic tension-type headache, thisis not so for severe episodic and chronic tension-type headache, wheresensitization of second order neurons occurs. In these patients,desensitization of these neurons should be the major target for drugintervention. It may, however, be difficult to desensitize these neuronsin face of an ongoing vigorous input from the periphery. Therefore,drugs which reduce peripheral sensitization may be needed in addition tothe drugs which desensitize second order nociceptive neurons, or drugsworking at both levels may be needed. Preferably, treatment should begiven early enough to prevent sensitization of second order neurons.Alternatively, if marked sensitization at the cortical level occurs, theindividual being hypersensitive to painful stimuli all over the body, itmay not be enough to intervene against the sensitization of second orderneurons. For such patients intervention against cortical sensitizationis recommended as an additional measure.

The Novel Therapeutic Principle According to the Invention For Treatmentof Tension-type Headache

According to the present invention, several means of intervening againsttension-type headache can b, envisaged, depending on the level accordingto the above, at which the intervention is aimed. In either case. be itin the periphery, the second order neurons of the sensory trigeminalnucleus or the cortex, the intervention must target the transmission ofnerve impulses. A number of different transmitter substances areinvolved in this transmission at each level. Thus, the invention, insome of its aspects, relate to the following therapeutic principles intension-type headache of the chronic type and of the severe episodictype defined as having headaches ten or more days per month:

Administration of agents or drugs (in the present specification andclaims, the terms agent and drug are used as interchangeable) whichprevent or reduce sensitization of second order nociceptive neuronslocated in the nucleus of the descending tract of the trigeminal nerveand in the C2 and C3 segments of the dorsal cervical horn of the spinalcord. There are several known types of assays indicating the capabilityof an agent to prevent or reduce central sensitization. In thefollowing, 13 such assays are described.

Administration of agents or drugs which reduce supraspinal painsensitization to a normal level. These are agents or drugs whichnormalize the response of pressure pain thresholds in the temporalregion to tooth clenching and drugs which normalize pain thresholds inhand.

Administration of agents or drugs which reduce peripheral sensitizationdefined as agents or drugs which prevent the development of abnormaltenderness due to tooth clenching.

Administration of agents or drugs which normalize the pain response tointra muscular infusion of bradykinin, 5-HT, histamine, prostaglandinesand/or nitroglycerine.

Administration of agents or drugs which normalize local pressure painthreshold over myofascial tissues of the head.

Administration of agents or drugs which have more than one of the aboveeffects.

Administration of agents or drugs which in a panel of test patients withtension-type headache have one of the above effects described one byone.

When targeting the transmission of nerve impulses according to theinvented model, it is preferred to interact with the followingsubstances relating to neurotransmission in connection with pain:

Glutamate

Substance P

Nitric oxide

GABA

It is particularly preferred to:

Antagonize the effect of glutamic acid

Antagonize the effect of substance P

Antagonize the effect of nitric oxide

Stimulate the effect of GABA.

More specifically, it is preferred to use:

NMDA receptor antagonists

Inhibitors of neuronal nitric oxide synthase (NOS)

GABA A and GABA B receptor agonists

Counteraction of Central Sensitization of Second Order Neurons

In order to counteract central sensitization of second order neurons ofthe sensory trigeminal nucleus/dorsal horn, it will be advantageous tocause a decrease in neuronal transmission involving the pathwaysutilizing e.g. the transmitter substances glutamate, nitric oxide, andthe neurokinins (substance P, bradykinin, neurokinin A, neurokinin B).Also, it will be of interest to counteract the action of secondmessengers such as guanylate cyclase, cGMP as well as any further stepsin the action of cGMP in second order sensory neurons receivingnociceptive input from the head and neck.

Prevention of central sensitization of second order neurons

In order to prevent the occurrence of central sensitization of secondorder neurons of the sensory trigeminal nucleus/dorsal horn, it will beadvantageous to normalize neuronal transmission in the peripheral and/orcentral nervous system involving transmitter substances such asglutamate, GABA, adenosine, nitric oxide, the neurokinins (substance P,bradykinin, neurokinin A, neurokinin B), neurotrophins and histamine.While it might have seemed advantageous to use 5-HT_(1D) receptoragonists because they stabilize presynaptic nociceptive terminals,studies by the inventors have shown that a compound of this class(sumatriptan) is not effective to a clinically relevant extent intension-type headache although it is highly effective in migraine(Brennum et al. 1992, 1996). Counteracting excitatory 5-HT receptors,such as 5-HT₂ and 5-HT₃ localized on second order neurons, however, arecontemplated to be effective in the treatment of tension-type headachein accordance with the present invention.

DETAILED DESCRIPTION OF THE INVENTION

On the basis of their experimental discoveries and analyses, the presentinventors have devised, for the first time, a strategy for the treatmentor prevention of tension type headache. Up to now, there has not beenany effective treatment available for tension type headache, which hasbeen a very serious problem in view of the very high prevalence oftension-type headache.

The present invention relates to a method of treatment or prevention oftension-type headache in a person in need of such treatment, the methodcomprising administering an amount of an agent effective to interactwith neuronal transmission connected with pain perception so as toprevent or reduce central sensitization.

The attainment of prevention or reduction of central sensitization canbe demonstrated by one of the following assays:

1) Normalization of a pathological qualitatively alteredstimulus-response function. The attainment of a normalization of aqualitatively altered stimulus-response function in connection withnociception (Bendtsen et al. 1996c, Example 1) can be demonstrated bypalpation of the trapezius muscle and recording of the degree of paincorresponding to the intensity of palpation (Bendtsen et al. 1994). Whena curve representing the stimulus/response function in connection withnociception has changed in shape from being substantially linear in anormal representation to being substantially linear in a doublelogarithmic representation, a normalization of the qualitatively alteredstimulus/response function has been obtained. In the present context, anagent which normalizes a qualitatively altered stimulus-responsefunction in connection with nociception is an agent which, whenadministered to a group of at least 20 patients suffering fromtension-type headache, will cause the curve representing thestimulus/response function in connection with nociception to becomesubstantially linear when represented double logarithmically in at least10 of the patients. Preferably, the agent so defined has such an effectin at least 12 of the patients. More preferably, the agent so definedhas such an effect in at least 14 of the patients.

2) Normalization of a pathological abnormally low pain threshold. Theattainment of a normalization of an abnormally low pain threshold can bedemonstrated by the measurement of the pressure pain threshold in theextremities or in the pericranial region with an electronic pressurealgometer or by the measurement of the electrical pain threshold with aconstant current stimulator as previously described (Bendtsen et al.1996a). When the pain threshold has changed from being significantlylower in a group of patients with tension-type headache than in a groupof healthy controls to be not significantly different between the twogroups, a normalization of the abnormally low pain threshold has beenobtained. In the present context, an agent which normalizes anabnormally lov pain threshold is an agent which, when administered to agroup of at least 10 patients suffering from tension-type headache, willchange the pain threshold from being significantly lower than that in agroup of healthy controls to be not significantly different between thetwo groups.

3) Reduction of a pathological pericranial muscle hardness. Theattainment of reduction of pericranial muscle hardness can bedemonstrated by the measurement of hardness in the pericranial muscleswith a hardness meter as previously described (Ashina et al. 1998a).When the muscle hardness is reduced significantly more following theadministration of a given agent than following the administration ofplacebo, a reduction of muscle hardness has been obtained. In thepresent context, an agent which reduces pericranial muscle hardness isan agent which, when administered to a group of at least 10 patientssuffering from tension-type headache, swill reduce pericranial musclehardness significantly more than placebo. Such a reduction willtypically be at least 10%. Preferably the reduction will be at least20%. More preferably the reduction will be at least 30%.

4) Reduction of a pathological increased pericranial myofascialtenderness. The attainment of reduction of increased pericranialmyofascial tenderness can be demonstrated by the measurement of thetenderness in the pericranial region using the Total Tenderness Scoringsystem as previously described (Bendtsen et al. 1995). Myofascialtenderness is considered to be increased when the Total Tenderness Scoreor the Local Tenderness Score in the pericranial region is above the 75%percentile of the Total Tenderness Score or the Local Tenderness Scorein a group of healthy controls (Jensen and Rasmussen 1996). In thepresent context, an agent which reduces increased pericranial myofascialtenderness is an agent which, when administered to a group of at least10 patients suffering from tension-type headache, will reduce the TotalTenderness Score or the Local Tenderness Score in the pericranial regionby at least 10% compared with the administration of placebo. Preferably,the agent so defined will reduce the Total Tenderness Score or the LocalTenderness Score in the pericranial region by at least 20% compared withthe administration of placebo. More preferably, the agent so definedwill reduce the Total Tenderness Score or the Local Tenderness Score inthe pericranial region by at least 30% compared with the administrationof placebo.

5) Prevention or reduction of pain, tenderness or hardness inpericranial muscles, or prevention or normalization of a qualitativelyaltered stimulus-response function or a reduced pain threshold inducedby experimental tonic muscle contraction. The attainment of preventionor reduction of pain, tenderness or hardness, or prevention ornormalization of a qualitatively altered stimulus-response function or areduced pain threshold can be demonstrated as described in assays 1-4above. Experimental tonic muscle contraction can be obtained byclenching of the molar teeth for 30 minutes at 10% of the individualsubject's maximal voluntary contraction measured from electromyographicrecordings of the activity in the temporal or masseter muscles aspreviously described (Jensen and Olesen 1996). In the present context,an agent which prevents or reduces pain, tenderness or hardness, orprevents or normalizes a qualitatively altered stimulus-responsefunction or a reduced pain threshold induced by experimental tonicmuscle contraction is an agent which, when administered to a group of atleast 10 human subjects, will prevent or reduce pain, tenderness orhardness, or prevent or normalize a qualitatively alteredstimulus-response function or a reduced pain threshold induced byexperimental tonic muscle contraction to a significantly higher degreethan placebo.

6) Prevention or reduction of pain, tenderness or hardness inpericranial muscle, or prevention or normalization of a qualitativelyaltered stimulus-response function or a reduced pain threshold inducedby intra muscular infusion of algogenic substances. The attainment ofprevention or reduction of pain, tenderness or hardness, or preventionor normalization of a qualitatively altered stimulus-response functionor a reduced pain threshold can be demonstrated as described in assays1-4 above. Intra muscular infusion of algogenic substances can beperformed by the use of a 0.4 mm needle as previously described (Jensenet al. 1990). Algogenic substances such as bradykinin, serotonin,histamine, adenosine-tri-phosphate, prostaglandines, capsaicin,hypertonic saline, potassium, nitroglycerine or combinations hereof canbe used. The algogenic substances can be injected either as a singlebolus injection (Jensen et al. 1990) or as a prolonged infusion (Zhanget al. 1993). In the present context, an agent which prevents or reducespain, tenderness or hardness, or prevents or normalizes a qualitativelyaltered stimulus-response function or a reduced pain threshold inducedby intra muscular infusion of algogenic substances is an agent which,when administered to a group of at least 10 human subjects, will preventor reduce pain, tenderness or hardness, or prevent or normalize aqualitatively altered stimulus-response function or a reduced painthreshold induced by intra muscular infusion of algogenic substances toa significantly higher degree than placebo.

7) Prevention or reduction of pain, tenderness or hardness inpericranial muscle, or prevention or normalization of a qualitativelyaltered stimulus-response function or a reduced pain threshold inducedby stimulation of nociceptive afferents in myofascial tissues. Theattainment of prevention or reduction of pain, tenderness or hardness,or prevention or normalization of a qualitatively alteredstimulus-response function or a reduced pain threshold can bedemonstrated as described in assays 14 above. Stimulation of nociceptiveafferents in myofascial tissues can be obtained by methods such aseccentric muscle contraction (Howell et al. 1993), prolonged staticmuscle contraction, repeated monotonous muscle work, ischemic muscleexercise (Myers and McCall Jr 1983), electrical stimulation via needleelectrodes inserted into the muscles (Vecchiet et al. 1988) ormechanical pressure applied to the muscles. In the present context, asubstance which prevents or reduces pain, tenderness or hardness, orprevents or normalizes a qualitatively altered stimulus-responsefunction or a reduced pain threshold induced by stimulation ofnociceptive afferents in myofascial tissues is a substance which, whenadministered to a group of at least 10 human subjects, will prevent orreduce pain, tenderness or hardness, or prevent or normalize aqualitatively altered stimulus-response function or a reduced painthreshold induced by stimulation of nociceptive afferents in myofascialtissues to a significantly higher degree than placebo.

8) Prevention or reduction of secondary allodynia or secondaryhyperalgesia induced by stimulation of nociceptive afferents inmyofascial tissues. The attainment of prevention or reduction ofsecondary allodynia or secondary hyperalgesia can be demonstrated bymeasuring pain sensitivity in the unaffected tissue area that surroundsan area in which nociceptive afferents are stimulated (Magerl et al.1998). Pain sensitivity can be measured by visual analogue scalerecording of the pain intensity evoked by stimuli such as mechanicalpressures applied by an electronic pressure algometer, manual palpationor pressure-controlled palpation (Bendtsen et al. 1995; Bendtsen et al.1996a), punctuate mechanical stimuli applied by von Frey hairs (Magerlet al. 1998), light touch stimuli applied by a soft cotton wisp (Magerlet al. 1998), thermal stimuli applied by the Marstock thermotest(Nørregaard et al. 1997) or electrical stimuli applied by surfaceelectrodes (Bendtsen et al. 1996a) or intra muscular needle electrodes(Vecchiet et al. 1988) or by measuring the nociceptive flexion reflex(Willer et al. 1984). Stimulation of nociceptive afferents in myofascialtissues can be obtained as described in assays 5-7 above. In the presentcontext, an agent which prevents or reduces secondary allodynia orsecondary hyperalgesia induced by stimulation of nociceptive afferentsin myofascial tissues is an agent which. when administered to a group ofat least 10 human subjects, will prevent or reduce secondary allodyniaor secondary hyperalgesia induced by stimulation of nociceptiveafferents in myofascial tissues to a significantly higher degree thanplacebo.

9) Prevention or reduction of wind-up induced by repetitive stimulationof nociceptive afferents in the pericranial region. The attainment ofprevention or reduction of wind-up can be demonstrated by measuring painsensitivity to repeated stimuli (Magerl et al. 1998), since temporalsummation of painful stimuli is regarded as a psychophysical correlateof wind-up (Price et al. 1994). In the present context, wind-up isdefined to be present when repeated identical stimuli becomeincreasingly painful (Pedersen et al. 1998). Wind-up can be induced bystimuli such as repeated electrical stimuli, e.g. five stimuli of 1 msduration with an intensity of 1.4 times the baseline pain thresholddelivered at 2 Hz by a constant current stimulator (Pedersen et al.1998), or as repeated punctuate mechanical stimuli, e.g. five stimulidelivered at 2 Hz with a 256 mN calibrated von Frey hair (Magerl et al.1998). The evoked pain intensity can be measured using a visual analoguescale. In the present context, an agent which prevents or reduceswind-up induced by stimulation of nociceptive afferents in thepericranial region is an agent which, when administered to a group of atleast 10 human subjects, will prevent or reduce wind-up induced bystimulation of nociceptive afferents in the pericranial region to asignificantly higher degree than placebo.

10) Prevention or reduction of secondary allodynia or secondaryhyperalgesia Induced by nociceptive input in an experimental animalmodel. The degree of secondary allodynia or secondary hyperalgesia canbe examined by measuring pain sensitivity in the unaffected tissue areathat surrounds an area in which nociceptive afferents are stimulated(Magerl et al. 1998). Pain sensitivity can be measured by recording theresponse of the animal to well-defined stimuli e.g. briskly stroking theskin with the blunt point of a pencil (Magerl et al. 1998), mechanicalpressures applied by an electronic pressure algometer, manual palpation,pressure-controlled palpation or calibrated von Frey hairs Mao et al.1992), electrical stimuli or thermal stimuli (Hao et al. 1992). Theresponse of the animal can be measured by methods such as: a) grading ofthe behavior of the animal to avoid a given stimulus, e.g. as a score of0: no response; 1: moderate efforts to avoid the stimulus; and 2:vigorous efforts to escape the stimulus (Hao et al. 1992); b) recordingthe time required for eliciting a given response of the animal, e.g.withdrawal of an extremity, by a given stimulus (Hao et al. 1992); c)recording the intensity of a stimulus that elicits a given reaction,e.g. vocalization or withdrawal or licking of an extremity (Hao et al.1992); or d) by a combination of the above-mentioned methods (Hao et al.1992). The induction of secondary allodynia or secondary hyperalgesiacan be performed as described above in, assays 6 and 7 or by methodssuch as the application to the skin of chemical irritants, e.g. mustardoil (Woolf and King 1990), thermal stimuli (Hylden et al. 1989),pinching, subcutaneous or intra muscular injections of complete Freund'sadjuvant (Hylden et al. 1989). In the present context, an agent whichprevents or reduces secondary allodynia or secondary hyperalgesiainduced by nociceptive input in an experimental animal model is an agentwhich will prevent or reduce secondary allodynia or secondaryhyperalgesia induced by nociceptive input in an experimental animalmodel to a significantly higher degree than placebo.

11) Prevention or reduction of wind-up induced by repetitive stimulationof nociceptive afferents in an experimental animal model. The degree ofwind-up can be examined by measuring pain sensitivity (Magerl et al.1998) or the activity of second order neurons to repeated stimuli (Woolfand Thompson 1991). In the present context, wind-up is defined to bepresent when repeated identical stimuli become increasingly painfulPedersen et al. 1998) or potentiate the responses of second orderneurons (Laird et al. 1995). Pain sensitivity in animals can be recordedas described above in assay 10, while the activity of second orderneurons can be measured using extra- and intracellular recordings of theactivity in these neurons (Woolf and King 1990; Hu et al. 1992). Afterexposure of the spinal cord via laminectomy, extracellular recordingscan be made using glass microelectrodes and intracellular recordings canbe made using potassium acetate electrodes (Woolf and King 1990).Wind-up can be induced by stimuli such as those described in assay 10.In the present context, an agent which prevents or reduces wind-upinduced by repetitive stimulation of nociceptive afferents in anexperimental animal model is an agent which will prevent or reducewind-up induced by repetitive stimulation of nociceptive afferents in anexperimental animal model to a significantly higher degree than placebo.

12) Prevention or reduction of increased receptive field size of secondorder neurons induced by nociceptive input in an experimental animalmodel The receptive field size of second order neurons can be measuredusing extra- and intracellular recordings of the activity in theseneurons (Woolf and King 1990;Hu et al. 1992) as described above in assay11. The receptive fields can be mapped using stimulation with, e.g.,calibrated von Frey hairs, blunt probes (Hylden et al. 1989), thermalstimuli (Hylden et al. 1989), serrated forceps or calibrated pinchersapplied to the skin (Woolf and King 1990). The induction of increasedreceptive field size of second order neurons can be performed asdescribed above in assay 10. In the present context, an agent whichprevents or reduces increased receptive field size of second orderneurons induced by nociceptive input in an experimental animal model isan agent which will prevent or reduce increased receptive field size ofsecond order neurons induced by nociceptive input in an experimentalanimal model to a significantly higher degree than placebo.

13) Prevention or reduction of increased excitability of the flexionreflex induced by nociceptive input in an experimental animal model Theexcitability of the flexion reflex can be examined by measuring theactivity in flexor motor neurons elicited by a standard stimulus appliedipsilaterally to the recording of flexor motor neuron activity (Woolf1983). The examination can, e.g., be performed by extracellularrecordings of the activity from flexor alpha motor neurons to theposterior biceps femoris/semitendinosus muscles in the decerebrate rat(Woolf and Thompson 1991). The flexion reflex can, e.g., be elicited bya standard pinch applied to the ipsilateral toes (Woolf and Thompson1991). The induction of increased excitability of the flexion reflex canbe performed as described above in assay 10. In the present context, anagent which prevents or reduces increased excitability of the flexionreflex induced by nociceptive input in an experimental animal model isan agent which will prevent or reduce increased excitability of theflexion reflex induced by nociceptive input in an experimental animalmodel to a significantly higher degree than placebo.

Prevention or Reduction of Central Sensitization Induced By NociceptiveInput in an Experimental Animal Model.

The degree of central sensitization in an experimental animal model canbe measured by other methods which are presumed to reflect centralsensitization but which are not mentioned in the above described assays10-13, i.e. measurement of cellular intermediate early genes such asc-fos (Dubner and Ruda 1992). The induction of central sensitization canbe performed as described above in assay 10. In the present context, anagent which prevents or reduces central sensitization induced bynociceptive input in an experimental animal model is an agent which willprevent or reduce central sensitization induced by nociceptive input inan experimental animal model to a significantly higher degree thanplacebo.

In the present context the term “significantly higher degree thanplacebo” should be taken to mean statistically significant when therelevant statistical tests are applied to data relating to an effect ofan agent according to the invention compared to an effect of placebo inany given assay or test.

The interaction with neuronal transmission connected with painperception will normally be interaction with neuronal transmissionconnected with second order nociceptive neurons. This interaction willnormally involve prevention of sensitization by way of a reduction ofC-fiber input to the second order nociceptive neurons or reversal of analready established sensitization of second order nociceptive neurons.

Interaction with neuronal transmission connected with pain perceptioncan be exerted by increasing inhibitory synaptic stimuli or it can beexerted by decreasing excitatory synaptic stimuli.

By the term “palpation” is meant the act of applying, faith the fingers,pressure to the surface of the body for the purpose of determining theamount of pain elicited in the underlying tissue by said pressureintensity.

In the present context, the term “qualitatively alteredstimulus/response function” in connection with nociception means thatthe function describing the amount of pain elicited by a given pressureintensity, sensed by a person being palpated, has changed in shape frombeing positively accelerating to being substantially linear, of Example1.

By the term “tender muscle” is meant a muscle in which pain is elicitedby palpation with a clinically relevant pressure.

In the present context, by the term “central sensitization” is meantthat second order nociceptive neurons residing in the central nervoussystem are rendered more sensitive than normally to incoming synapticstimuli. At the occurrence of central sensitization such stimuli willelicit excitation of the said central neurons at stimulation below thenormal threshold for excitation; thus, central neurons possess anincreased excitability.

In the present context, myofascial pain relates to pain in themyofascial tissue, by which is meant muscular structures, tendons andtendon insertions related to the pericranial and cervical region.

In the context of the present invention second order nociceptive neuronsare neurons located in the nucleus of the trigeminal tract and of C2 andC3 segments of medullary dorsal horns, said neurons being involved inthe processing of nociceptive stimuli.

By the term “C-fibers” is meant a class unmyelinated nociceptive fibersterminating on neurons in the nucleus of the trigeminal tract/dorsalhorn of the spinal cord.

The interaction with neuronal transmission connected with painperception, so as to obtain a substantial prevention or a substantialnormalization of an otherwise qualitatively altered stimulus-responsefunction in connection with nociception is preferably performed byadministering an effective amount of an agent which prevents ornormalizes an otherwise qualitatively altered stimulus response functionin connection with nociception.

In the present context, an agent which prevents or normalizes anotherwise qualitatively altered stimulus-response function in connectionwith nociception is an agent which, when administered to a group of atleast 20 patients suffering from tension type headache as defined above,will cause the curve representing the stimulus/response function inconnection with nociception to become substantially linear whenrepresented double logarithmically in at least 10 of the patients.Preferably the agent so defined has such an effect in at least 12 of thepatients. More preferably the agent so defined has such an effect in atleast 14 of the patients.

A number of substances and classes of substances which interact withneuronal transmission to exert this function are known, confer thedetailed discussion thereof in the following.

In accordance with what is explained above, another way of expressingthe treatment according to the invention is by reference to painthreshold in connection with chronic contraction of muscle, inparticular tooth clenching. Thus, according to this, the invention canbe expressed as a method for treatment of tension-type headache in aperson in need of such treatment, comprising interacting with neuronaltransmission connected with pain perception so as to obtain asubstantial increase of an otherwise unresponsive pain threshold inconnection with chronic contraction of muscle, in particular toothclenching.

Again, the interaction is preferably performed by administering an agentwhich will interact with neuronal transmission in a manner correspondingto what has been described above. The agent can be characterized as aagent which performs positively (as described above), in one or more ofthe assays described above, such as the stimulus/response function testdescribed above, or as a agent which, in a group of at least 20 patientssuffering from tension tape headache as defined above, will cause theeffect of tooth clenching to be an increased pain threshold instead ofan abnormally low pain threshold in at least 10 of the patients,preferably at least 12 of the patients, more preferably in at least 14of the patients.

In another aspect, the invention relates to an agent having theproperties defined herein for use as a medicament, in particular for thetreatment of tension-type headache. This aspect relates to thosesubstances or substance classes discussed herein which have notpreviously been used as medicaments or diagnostics.

In a further aspect, the invention relates to the use of an agent havingthe properties described herein for the preparation of a pharmaceuticalcomposition for the treatment or prevention of tension-type headache.

In one aspect of the present invention the treatment or prevention oftension-type headache according to the invention is not accompanied by asubstantial reduction of muscle tension.

In an important aspect the present invention relates to a method fortreating tension-type headache in a person which comprises administeringan agent in an amount effective to alleviate said headache, said agentbeing an agent capable of altering the relationship of pain intensity topressure intensity when the trapezoid muscle is palpated at differentpressure intensities in said person. The relationship is typicallysubstantially linear in the untreated persons, and substantiallynon-linear in the treated persons. Furthermore, the relationship willtypically be positively accelerating in the treated person. In oneembodiment of the present invention the rate of acceleration of painintensity with pressure intensity is substantially constant. In oneimportant embodiment of the present invention the relationship in thetreated persons is substantially the same as in control persons who didnot have tension-type headache and who were treated with a placebo.

The agent interacting with neuronal transmission to substantiallynormalize an otherwise qualitatively altered stimulus/response functionin connection with nociception is preferably one which directlyquantitatively lowers pain perception, in that, in a panel of testpersons suffering from increased myofascial tenderness with disorder ofpericranial muscle in connection with tension-type headache, theadministration of the agent will result in transformation of asubstantially linear pain intensity perception in response to pressureintensity in trapezius as well as other relevant pericranial musclesinto a cure (C) of which the values of pain intensity are lower than thelinear pain intensity perception.

The curve (C) is preferably a curve which can be described substantiallyas a power function and is a curve which is substantially linear in adouble logarithmic plot.

It is preferred that substantially each of the values of curve (C) is atthe most 20% higher, preferably at the most 10% higher, than the valueof the corresponding curve produced for a test panel of healthycontrols.

In connection with any of the patient panel tests discussed above it isnoted that the treatment with the agent in question should be performedby administration at least once daily to maintain a therapeutic plasmalevel in the patients and should be continued for a sufficient time toallow the agent to exert its therapeutic effect, but that an agent isconsidered not to perform according to the particular test if the effectis not obtained within a treatment time of three months. This does notmean that it will necessarily take three months for an agent to exertits therapeutic effect; some compounds will show their therapeuticeffect after much shorter treatment periods, down to days or even hours.In connection with testing of a new candidate agent, the dosage of theagent will normally be kept as high as permitted by the toxicity of thecompound during initial tests and will then be reduced to a lower levelwhich is still maximally effective during the test proper.

Evaluation of the ability of an agent to provide an effective treatmentfor tension-type headache, by interacting with neuronal transmissionaccording to the present invention, may also be performed as an acutetest, in which the agent is administered, typically as a bolus or aninfusion, to a group of patients suffering from chronic tension-typeheadache. In such a test, the pain connected to tension-type headache inthese patients will typically be scored by the patients, as described inexample 4, at various time points after administration of the agent,typically at least every 15 rain and subsequently monitored over aperiod of at least 30 min, typically at least 60 min, preferably atleast 90, more preferably at least 120 min. For the evaluation of acandidate agent, an additional group of patients acutely suffering fromtension-type headache will receive placebo and serve as a control group.The curves based on the pain scores of patients in both groups willtypically be compared, as shown in FIG. 14, and an agent will beconsidered effective in treatment of tension-type headache according tothe present invention, if it is capable of preventing or substantiallypreventing pain in connection with tension-type headache when painscores after administration of the agent, when differering most from thecorresponding score after administration of placebo, are at least 10%lower than scores for placebo, typically at least 20% lower, preferablyat least 30% lower, more preferably at least 40% lower. For anevaluation as described here, the size of the participating groups ofpatients will be at least 5 patients in each group, typically at least 7patients in each group, preferably at least 10 patients in each group,more preferably at least 12 patients in each group, even more preferablyat least 15 patients in each group.

Evaluation of the ability of an agent to provide an effective preventionof tension-type headache by interacting with neuronal transmissionaccording to the present invention can be performed as described aboveexcept that the parameter measured and scored by headache patients willtypically be duration of pain or frequency of pain in connection withtension-type headache in sufferers with an episodic form of the disease.

In the practical treatment of a patient, the administration of an agentwill normally be continued for at least one month, preferably at leasttwo months and more preferably at least three months and in many casesindefinitely in order to establish and maintain the normalization whichis aimed at. If the desired normalization occurs before one month oftreatment, it is certainly possible according to the invention todiscontinue the treatment, but this will increase risk of relapse and isnormally not preferred. The administration is performed using at leastone dose daily or at any rate substantially at least one dose daily(which means that the treatment is not outside the scope of theinvention if it is just interrupted one or perhaps even (but notpreferred) a few days), and the dose of the particular agent ispreferably adapted so that it will maintain a therapeutic plasma levelsubstantially at any time. Notwithstanding the above statement to theeffect that the administration may in many cases be performedindefinitely, it is contemplated that there will be cases where thetreatment period will be less than 10 years, such as less than 5 yearsor less than 2 years or even less than 1 year.

The interaction with neuronal transmission connected with painperception will normally be such an interaction with neuronaltransmission connected with second order nociceptive neurons whichinvolves substantially reducing excitation mediated through theinteraction between transmitter substances and their receptors on secondorder nociceptive neurons.

The above-mentioned interaction will normally involve a reduction ofC-fiber, A-d-fiber and A-b-fiber input to the nociceptive second orderneurons, through a substantial reduction of excitatory activity insynapses of C-fibers, A-d-fibers and A-b-fibers on second order neurons,said activity mediated through the interaction between the involvedtransmitter substances and their receptors on second order nociceptiveneurons.

The reduction of excitatory activity in synapses of C-fibers, A-d-fibersand A-b-fibers on second order neurons mediated through the interactionbetween the involved excitatory transmitter substances and theirreceptors on second order nociceptive neurons will preferably beperformed by administration of an effective amount of at least one agentwhich a) substantially inhibits the production of said excitatorytransmitter substance, b) substantially inhibits the release of saidexcitatory transmitter substance, c) substantially counteracts theaction of said excitatory transmitter substance, and/or d) substantiallyinhibits the binding of said excitatory transmitter substance to itsrelevant receptors.

Important examples of such excitatory transmitter substances areselected from the group consisting of glutamate, nitric oxide,neurokinins (substance P, neurokinin A, neurokinin B and bradykinin),CGRP, adenosine working through 4A2 receptors, 5-HT when working through5-HT2.3 receptors and pituitary adenylate cyclase activating polypeptide(PACAP).

Agents which can interact with neuronal transmission mediated byglutamate will typically comprise competitive or non-competitiveantagonists of ionotropic glutamate receptors, including NMDA, AMPA andkainate receptors. Interaction with glutamate neurotransmission can alsobe performed with antagonists at the glycine site of the NODA receptorsor Faith antagonists or inverse agonists at modulatory sites such aspolyamine sites. Interaction with metabotropic glutamate receptors canbe performed with agonists or antagonists depending on whether they arereceptors located pre or postsynaptically and whether they belong to theexcitatory type I receptors (mGluR1,5) or the inhibitory type II andtype III receptors (mGluR2,3 and mGluR4,6-8, respectively).

While sensitization of second order neurons is believed, as explainedabove, to be an important cause of pain in connection with tension typeheadache, it is clear that other elements of neuronal transmission mayalso play a significant role and in some cases even a predominant roleas explained in the model described in connection with FIG. 1. Based onthis recognition, another, more general, aspect of the present inventionintroduces, for the first time, the use of a number of classes ofsubstances for treatment of tension type headache. This aspect relatesto a method for treatment or prevention of tension-type headache in aperson in need of such treatment, comprising administering an amount ofan agent which, in the peripheral and/or central nervous system, iseffective to specifically interact with neuronal transmission connectedwith pain perception by

a) substantially antagonizing the action of glutamate, 5-HT, GABA,nitric oxide, nitric oxide synthase, guanylate cyclase, cyclic guanylatemonophosphate (cGMP), CGRP, substance P, neurokinin A, neurokinin B,bradykidnin, PACAB, adenosine, glycine, histamine, neurotrophins,Na+ions or Ca²+ion channels,

or by

b) substantially potentiating the action of adenosine, galanine ornorepinephrine,

with the proviso that said agent is not ethyl2-amino-6-(4-fluorobenzylamino)-3-pyridylcarbamate or anarylglycineamide derivative as described herein.

An additional aspect of the present invention relates to a method oftreatment of tension-type headache comprising administering to a personin need of such treatment an effective amount of an agent whichsubstantially inhibits the action of the enzyme nitric oxide synthase(NOS) and thereby reduces chronic pain in connection with tension-typeheadache. In many cases the effect of treatment of tension-type headachewith a NOS inhibitor will be exerted through a decrease in existingcentral sensitization, but also within the scope of the invention istreatment of tension-type headache with NOS inhibitors whose effect onthe reduction of pain in connection with tension-type headache ismediated through a mechanism not directly involving inhibition ofcentral sensitization. Such an alternative mechanism might possiblycomprise an alteration of pain modulation involving nitric oxide.

A very important aspect of the present invention is a method ofscreening a drug for the ability to alleviate a tension-type headachewhich comprises comparing the relationship of pain intensity to pressureintensity when the trapezoid muscle is palpated at different pressureintensities for (a) persons having tension-type headaches aftertreatment with the drug, and (b) persons having tension-type headaches,treated with a placebo, and determining if the relationship is altered.Also within the scope of the present invention is a method of screeninga drug for the ability to alleviate tension-type headache comprisingtesting said drug in one or more of the assays 1-13 described above anddetermining effect in the test organism according to each assay. Thetest organisms will typically be human patients and human controls orrelevant experimental animals, depending on the given assay.

In the following discussion of substances or groups of substances,numbers in parenthesis refer to the correspondingly numbered structuralformulas in the formula sheets below.

Agents which inhibit neuronal transmission mediated by glutamate, in thecentral and/or peripheral nervous system, are capable of a)substantially inhibiting the production of glutamate, b) substantiallyinhibiting the release of glutamate, c) substantially counteracting theaction of glutamate and/or d) substantially inhibiting the binding ofglutamate to receptors for glutamate.

Examples of competitive NMDA receptor antagonists arenitrogen-containing heterocyclic compounds selected from diacidicpiperidines, such is CGS 19755 (1), diacidic piperazines, such as(R)-CPP (2) and (R)-CPPene (3), phosphono amino acids such as LY 235959(4) and derivatives of any of the above which are competitive NMDAantagonists or prodrugs thereof.

Examples of non-competitive NMDA receptor antagonists are polycyclicamines, such as M-801 (5); tricyclic antidepressants, such asMetapramine (6), Amitriptyline (7), Imipramine (8), Desipramine (9),Mirtazapine (10) or Venlafaxine (11); adamantanamines, such as Memantine(12); aryleyclohexylamines, such as Ketamine (13), arylcyclohexylamines,such as Norketamine (14); opioid derivatives, such Dextromethorphan(15); glycylamides, such as Remacemide (16): piperidinylethanols, suchas Ifenprodil (17); piperidinylethanols, such as Eliprodil (18);diguanidines, such as Syntlialin (19); γ-aminobutyric acid derivatives,such as Gabapentin (64); polycyclic amines, such as Pizotyline (83) orderivatives of any of the above which are non-competitive NMDAantagonists or prodrugs thereof.

Mirtazapine (10) and Venlafaxine (11) are conventionally known, to haveα-2 receptor antagonist effects, and their efficacy as antidepressantsare thought to be exerted through a decrease in noradrenergicneurotransmission. However, it is presently believed that Mirtazapineand Venlafaxine may also have an effect on glutamate neurotransmission,potentially as non-competitive NMDA receptor antagonists. It is throughthis mechanism that the two substances are presumed to provide a methodof treatment of tension-type headache according to the presentinvention.

Examples of Glycine antagonists are aminopyrrolidinones, such as(R)-HA-966 (20); kynurenic acid derivatives, such as 7-Cl-Kynurenic acid(21); tetrahydroquinolines, such as L-689,560 (22); kynurenic acidderivatives, such as L-701,252 (23), L-701,273 (24), L-701,324 (25);indoles such as GV15026A (26,); glycine derivatives, such as ACPC (27);quinoxalinediones, such as MNQX (28), ACEA 1021 (29) and DCQX (30);dicarbamates, such as Felbamate (31) and derivatives of any of the abovewhich are glycine antagonists or prodrugs thereof.

Examples of competitive AMPA receptor antagonists are quinoxalinediones,such as CNQX (32), NBQX (33), PNQX (34) and YM9OK (35);dihydroquinolones, such as L-698,544 (36); diacidicdecaliydroisoquinolines, such as LY 215490 (37); amino acid isoxazoles,such as AMOA (38); indoleoximes, such as NS-257 (39) and derivatives ofany of the above which are competitive AMPA receptor antagonists orprodrugs thereof.

Examples of non-competitive AMPA receptor antagonists are2,3-benzodiazepines, such as GYKI 52466 (40), phthalazines, such as SYNC2206 (41) and derivatives of any of the above which are noncompetitiveAMPA receptor antagonists or prodrugs thereof.

Examples of competitive kainate receptor antagonists are indoleoximes,such as NS-102 (42) and derivatives thereof which are competitive kainicacid receptor antagonists or prodrugs thereof.

Examples of metabotropic receptor agonists are phenylglycines, such as4CPG (43); amino acid indanes. such as UPF523 (44); phosphono aminoacids, such as L-AP4 (45) and derivatives of any of the above which aremetabotropic glutamate receptor agonists or prodrugs thereof.

Agents which inhibit neuronal transmission mediated by 5-HT, in thecentral and/or peripheral nervous systems, are capable of a)substantially inhibiting the synthesis of 5-HT, b) substantiallyinhibiting the release of 5-HT, c) substantially counteracting theaction of 5-HT and/or d) substantially inhibiting the binding of 5-HT toexcitatory 5-HT 5-HT, receptors.

Examples of 5-H1T_(2,3) receptor antagonists are tropan derivatives,such as Tropanserin (82); polycyclic amines, such as Pizotyline (83) andderivatives of any of the above which are 5-HT2,3 receptor antagonistsor prodrugs thereof.

It is presently believed that pizoryline (83) may also have effect onglutamate neurotransmission, potentially as a non-competitive NMDAreceptor antagonist, as mentioned above. This mechanism is presumed, inaddition to the 5-E receptor antagonism, to provide a method oftreatment of tension-type headache according to the present invention.

Agents which can inhibit neuronal transmission mediated by adenosine, inthe central and/or peripheral nervous system, are capable of a)substantially inhibiting the synthesis of adenosine, b) substantiallyinhibiting the release of adenosine, c) substantially counteracting theaction of adenosine, and/or d) substantially functioning as antagonistsat adenosine A2 receptors.

Examples of adenosine AX receptor antagonists are xanthine derivatives,such as DMPX (80) and derivatives thereof which are A2 receptorantagonists or prodrugs thereof.

Examples of adenosine uptake inhibitors are homopiperazine derivatives,such as Dilazep (81) and derivatives thereof which are adenosine uptakeinhibitors or prodrugs thereof.

Agents which can inhibit neuronal transmission mediated by substance P,in the central and/or peripheral nervous system are capable of a)substantially inhibiting the synthesis of substance P, b) substantiallyinhibiting the release of substance P, c) substantially counteractingthe action of substance P, and/or d) substantially inhibiting binding ofsubstance P to receptors for substance P.

Agents which can inhibit neuronal transmission mediated by neurokinin A,in the peripheral and/or central nervous system, are capable of a)substantially inhibiting the synthesis of neurokinin A, b) substantiallyinhibiting the release of neurokinin A, c) substantially counteractingthe action of neurokinin A, and/or d) substantially inhibiting bindingof neurokinin A to receptors for neurokinin A (NK₂ receptors).

Examples of neurokinin A (NK₂) receptor antagonists are peptidomimetics,such as SR48968 (37); peptidomimetics, such as GR 159897 (38) andderivatives thereof which are 4N2 receptor antagonists or prodrugsthereof.

Agents which can inhibit neuronal transmission mediated by bradykinin,in the peripheral and/or central nervous system, are capable of a)substantially inhibiting the production of bradykinin, b) substantiallyinhibiting the release of bradykinin, c) substantially counteracting theaction of bradykinin and/or d) substantially inhibiting binding ofbradykinin to receptors for bradykinin.

Examples of bradykinin receptor antagonists are peptidomimetics, such asIcatibant (48) and WIN 64338 (49) and derivatives of any of the abovewhich are bradykinin receptor antagonists or prodrugs thereof.

Agents which can inhibit neuronal transmission mediated by CGRP, in theperipheral and/or central nervous system, are capable of a)substantially inhibiting the production of CGRP, b) substantiallyinhibiting the release of CGRP, c) substantially counteracting theaction of CGRP and/or d) substantially inhibiting the binding of CGRP toreceptors for CGRP.

Examples of GCRP receptor antagonists are GCRP 8-37.

Agents which can inhibit neuronal transmission mediated by PACAP, in theperipheral and/or central nervous system are capable of a) substantiallyinhibiting the synthesis of PACAP, b) substantially inhibiting therelease of PACAP, c) substantially counteracting the action of PACAPand/or d) substantially inhibiting binding of PACAP to receptors forPACAP.

Agents which can inhibit neuronal transmission mediated by nitric oxide,in the peripheral and/or central nervous system, are capable of a)substantially inhibiting the production of nitric oxide b) substantiallycounteracting the action of nitric oxide, c) substantially inhibitingthe production of nitric oxide synthase (NOS) and/or d) substantiallycounteracting the action of nitric oxide synthase (NOS).

The interaction with neuronal transmission connected with painperception connected with second order nociceptive neurons call compriseinteraction with intracellular substances involved in this neuronaltransmission, said interaction involving excitation mediated through theinteraction with enzymes and second messengers in second ordernociceptive neurons.

Preferred examples or the above mentioned intracellular substances areNOS, guanylate cyclase, and cGMP.

The interaction with neuronal transmission connected with painperception, comprising interaction with NOS will preferably be performedby the administration of an effective amount of at least one agent whichcan substantially inhibit the production of the NOS, and/orsubstantially counteract the action of NOS.

Examples of NOS inhibitors are arginine derivatives, such as L-NAME(50), L-NMMA (51), L-NIO (52), L-NNA (53) and Dimethyl-L-arginine (54);citrulline derivatives, such as Thiocitrulline (55) and(S)-Methylthiocitrulline (56); indazoles, such as 7—Nitroindazole (57);imidazol in-N-oxides, such as Potassium carboxy-PTIO (58);phenylimidazoles, such as TRIM (59); 21-aminosteroids, such as Tirilazad(60); biphenyls, such as Diphenyleneiodinium chloride (61), piperidinederivatives, such as Paroxetine (62) and derivatives of any of the abovewhich are NOS inhibitors or prodrugs thereof.

The interaction with neuronal transmission connected with painperception, comprising interaction with guanylate cyclase can beperformed by the administration of an effective amount of at least oneagent which substantially inhibits the production of guanylate cyclaseand/or substantially counteracts the action of guanylate cyclase.

Examples of guanylate cyclase inhibitors are quinoxalines, such as ODQ(63) and derivatives thereof which are guanylate cyclase inhibitors.

The interaction with neuronal transmission connected with painperception comprising interaction with cGMP can be executed by theadministration of an effective amount of at least one agent which, inthe peripheral and/or central nervous system, is capable of a)substantially inhibiting the production of guanylate cyclase, b)substantially counteracting the action of guanylate cyclase, c)substantially inhibiting the production of cyclic guanylatemonophosphate (cGMP), d) substantially counteracting the action ofcyclic guanylate monophosphate (cGMP) and/or e) substantially inhibitingany further steps in the reaction induced by cyclic guanylatemonophosphate (cGMP), such as protein kinase C.

The activity of C-fibers, A-d-fibers and A-b-fibers on second ordernociceptive neurons involves inhibitory neurotransmitter substances.Reduction or activity of C-fibers on second order neurons till normallybe performed by administration of an effective amount of at least oneagent which is capable of a) substantially inhibiting the enzymaticdegradation of said inhibitory transmitter substance, b) substantiallyenhancing the release of said inhibitory transmitter substance, c)substantially enhancing the action of said inhibitory transmittersubstance and/or substantially activating the relevant receptor for saidinhibitory transmitter substance.

Preferred examples of such inhibitory transmitter substances areselected from the group consisting of GA BA, galanine, adenosine workingthrough A¹ receptors, and norepinephrine.

Agents which can stimulate neuronal transmission mediated by GABA, inthe peripheral and/or central nervous system, are capable of a)substantially enhancing the production of GABA, b) substantiallyinhibiting the enzymatic degradation of GABA, c) substantially enhancingthe release of GABA, d) substantially enhancing the action of GABAand/or e) substantially activating receptors for GABA.

An example of a substance with GABA-enhancing activity isbenzodiazepines, such as Midazolani (69) and derivatives thereof whichare GABA activity enhancers or prodrugs thereof.

Examples of GABA-A receptor agonists are γ-aminobutyric acidderivatives, such as Gabapentin (64) and TACA (65) Isonipecotic acid(66) and Isoguvacine (67); 3-hydroxyisoxazoles, such as THIP (68) andderivatives of any of the above which are GABA-A agonists or prodrugsthereof.

Gabapentin is conventionally known to have GABA-A receptor agonistactivity, though this mechanism has been questioned. However, it ispresently believed that Gabapentin may also have antagonist effect onglutamate transmission, indirectly or directly, potentially as anon-competitive NMDA receptor antagonist. as mentioned above. It isthrough this mechanism, in addition to its gabaergic activity, thatGabapentin is presumed to provide a method of treatment of tension-typeheadache according to the present invention.

Examples of GABA uptake inhibitors are carboxypiperidine derivatives,such as (±)-cis-4-Hydroxynipecotic acid (70); carboxypyridinederivatives, such as Guvacine (71): 3-hydroxyisoxazoles, such as THPO(72); nipecotic acid derivatives, such as SKF 89976-A (73) and Tiagabine(74); guvacine derivatives, such as NO-711 (75) and derivatives of anyif the above which are GABA uptake inhibitors or prodrugs thereof.

Examples of GABA transaminase inhibitors are 7-aminobutyric acidderivatives, such as Vigabatrin (76) and derivatives thereof which areGABA transminase inhibitors or prodrugs thereof.

Agents which can stimulate neuronal transmission mediated by galanine,in the peripheral and/or central nervous system, are capable of a)substantially inhibiting the enzymatic degradation of galanine, b)substantially enhancing the release of galanine, c) substantiallyenhancing the action of galanine and/or d) substantially functioning asagonists at galanine receptors.

Agents which can stimulate neuronal transmission mediated by adenosine,in the peripheral and/or central nervous system, are capable of a)substantially inhibiting the enzymatic degradation of adenosine, b)substantially enhancing the release of adenosine, c) substantiallyenhancing the action of adenosine and/or d) substantially functioning asagonists at A¹ receptors.

Examples adenosine A¹ receptor agonists are adenosine derivatives, suchas N⁶-Cyclopentyladenosine (77); adenilglucosides, such as Adenosine(78) and derivatives thereof which are Al receptor agonists or prodrugsthereof.

An example of an enhancer of the action of adenosine is pyrimidinederivatives, such as Dipyridamole (79) and derivatives thereof which areadenosine uptake inhibitors or prodrugs thereof.

Agents which can stimulate neuronal transmission mediated bynorepinephrine, in the peripheral and/or central nervous system, arecapable of a) substantially inhibiting the enzymatic degradation ofnorepinephrine, b) substantially enhancing the release ofnorepinephrine, c) substantially enhancing the action of norepinephrineand/or c) substantially functioning as agonists at norepinephrine α-2receptors.

Examples of a-2 receptor agonists are aminoimidazolines, such asClonidine (84); aminoimidazolines, such as Apraclonidine (85);thiazinamines, such as Xylazine (86); imidazoles, such asDexmedetomidine (87) and derivatives of any of the above which are α-2receptor agonists or prodrugs thereof.

Reduction of activity of C-fibers on second order nociceptive neuronscan be performed by administration of an effective amount of at leastone agent which substantially blocks ion channels for Na⁺ or Ca²⁺ ions.

Examples of Na⁺ channel blockers are triazines, such as Lamotrigine(88); diphenylmethylpiperazines, such as Lifarizine (89); hydantoins,such as Phenytoin (90); aminopiperidines, such as Lubeluzole (91);benzthiazoles, such as Riluzole (92); dibenzazepines, such asCarbamazepine (93); phenylamides, such as Lidocaine (94); phenylamides,such as Tocainide (95); aminoethylanisoles, such as Mexiletene (96) andderivatives of any of the above which are Na⁺ channel blockers orprodrugs thereof.

Examples of Ca²⁺ channel blockers are diphenylmethylpiperazines, such asFlunarizine (97); arylphosphonic esters, such as Fostedil (98) andderivatives of any of the above which are Ca²⁺ channel blockers orprodrugs thereof.

In accordance with normal usage, the tern “agent”, as used herein, isintended to designate an active substance per se, whether administeredas such or in the form of a prodrug thereof, as well as a pharmaceuticalcomposition comprising the substance or prodrug.

In addition to the specific substances mentioned above, derivativesthereof which show an activity of the same kind as the substancespecifically mentioned are also useful for the purpose of the presentinvention. The kind of derivatives which come into consideration evillyof course, depend on the specific character of the substance inquestion, but as general examples of derivatives which may be relevantfor many of the substances may be mentioned introduction of or change ofalkylsubstituents (typically with a chain length from one to five carbonatoms) on aliphatic chains, cycloalanes, aromatic and heterocyclic ringsystems, introduction of or change of substituents such as halogens ornitro groups, change of ringsize for cycloalkanes, change of aromatic orheterocyclic ringsystems, change of alkylsubstituents on O-and N-atoms,change of the alcohol part of ester groups, and bioisosteric replacementof functional groups, especially use of carboxylic acid bioisosteressuch as phosphonic acids, phosphinic acids, tetrazoles,3-hydroxyisoxazoles, sulphonamiders and hydroxyamic acids. Salts ofacidic or basic compounds will be equally useful compared to the freeacids or free bases. In case of raceric compounds, can racemates as wellas pure enantiomeres and diastereoisomeres be used, and in the case ofsubstances interacting with antagonist action be required. Of course,derivatives to be used should be derivatives which, in addition to theirdesired activity, show an acceptably low toxicity, and, in general, thederivates should, just as the substances themselves, be pharmaceuticallyacceptable.

The agent used according to the invention may be administered as such orin the form of a suitable prodrug thereof. The term “prodrug” denotes abioreversible derivative of the drug, the bioreversible derivative beingtherapeutically substantially inactive per se but being able to convertin the body to the active substance by an enzymatic or non-enzymaticprocess.

Thus, examples of suitable prodrugs of the substances used according tothe invention include compounds obtained by suitable bioreversiblederivatization of one or more reactive or derivatizable groups of theparent substance to result in a bioreversible derivative. Thederivatization may be performed to obtain a higher bioavailability ofthe active substance, to stabilize an otherwise unstable activesubstance, to increase the lipophilicity of the substance administeredetc.

Examples of types of substances which may advantageously be administeredin the form of prodrugs are carboxylic acids, other acidic groups andamines, which may be rendered more lipophilic by suitable bioreversiblederivatization. As examples of suitable groups may be mentionedbioreversible esters or bioreversible amides. Amino acids are typicalexamples of substances which, in their unmodified form, may have a lowabsorption upon administration. Suitable prodrug derivatives of aminoacids will be one or both of the above-mentioned types of bioreversiblederivatives.

For the administration to a patient, a substance having any of theactivities as defined above or a prodrug thereof is preferablyformulated in a pharmaceutical composition containing one or moresubstances having any of the activities as defined above or prodrugsthereof and one or more pharmaceutically acceptable excipients.

The substance or substances to be administered may be formulated in thecompositions in pharmaceutically acceptable media, the character ofwhich are adapted to the chemical character of the substance. Thecompositions may be adapted for administration by any suitable method,for example by oral, buccal, sublingual, nasal, rectal or transdermaladministration. Substances which are suitable for oral administrationmay be formulated as liquids or solids, such as syrups, suspensions oremulsions, tablets, capsules and lozenges. A liquid compositions willnormally comprise a suspension or solution of the substance in asuitable liquid carrier or suitable liquid carriers, for example anaqueous solvent such as water, ethanol or glycerol, or a non-aqueoussolvent, such as polyethylene glycol or an oil. The composition may alsocontain a suspending agent, preservative, flavouring or colouring agent.A composition in the form of a tablet can be made using any suitablepharmaceutical carrier or carriers used for preparing solidformulations, for example pharmaceutical grades of mannitol, lactose,starch, magnesium stearate, sodium saccharin, talcum, cellulose,glucose, sucrose, magnesium carbonate, and the like. For oraladministration, a pharmaceutically acceptable non-toxic composition maybe formed by incorporating normally used excipients, such as thosecarriers previously listed, and generally 1-95% of active ingredient,that is, a substance used according to the invention or a prodrugthereof, often preferably 25-75% of the substance of the prodrug. Acomposition in the form of a capsule can be prepared using conventionalencapsulation procedures. Thus, e.g., pellets containing the substanceor prodrug in question may be prepared using any suitable carriers andthen filled into a hard gelatin capsule, or a dispersion or suspensioncan be prepared using any suitable pharmaceutical carrier or carriers,such as aqueous gums, celluloses, silicates or oils and the dispersionor suspension can be filled into a soft gelatin capsule.

Examples of parenteral compositions are solutions or suspensions of thesubstances or prodrugs in a sterile aqueous carrier or parenterallyacceptable oil, such as polyethylene glycol, polyvinyl pyrrolidone,lecithin, arachis oil or sesame oil. The compositions may containpharmaceutically acceptable auxiliary substances as required toapproximate physiological conditions, such as buffering agents, wettingagents, detergents, and the like. Additives nay also include additionalactive ingredients, e.g. bactericidal agents, or stabilizers. Ifdesired, the solution or suspension can be lyophilized and reconstitutedwith a suitable carrier such as a sterile aqueous carrier prior toadministration.

Compositions for nasal administration can be formulated, e.g., asaerosols, drops, gels and powders. For aerosol administration, thesubstance or prodrug is preferably supplied in finely divided form alongwith a surfactant and propellant. Typical percentages of the substanceor prodrug are 0.01-20% by weight, preferably 1-10%. The surfactantmust, of course, be non-toxic, and preferably soluble in the propellant.Representative of such surfactants are the esters or partial esters offatty acids containing from 6 to 22 carbon atoms, such as caproic,octanoic, lauric, palmitic, stearic, linoleic, linolenic, olesteric andoleic acids with an aliphatic polyhydric alcohol or its cyclic anhydridesuch as, for example, ethylene glycol, glycerol, erythritol, arbitol,mannitol, sorbitol, the hexitol anhydrides derived from sorbitol, andthe polyoxyethylene and polyoxypropylene derivatives of these esters.Mixed esters, such as mixed or natural glycerides may be employed. Thesurfactant may constitute 0.1-20% by weight of the composition,preferably 0.25-5%. The balance of the composition is ordinarilypropellant. Liquified propellants are typically gases at ambientconditions, and are condensed under pressure. Among suitable liquifiedpropellants are the lower alkanes containing up to 5 carbons, such asbutane and propane; and preferably fluorinated or fluorochlorinatedalkanes, fixtures of the above may also be employed. In producing theaerosol, a container equipped with a suitable valve is filled with theappropriate propellant, containing the substance according to theinvention and surfactant. The ingredients are thus maintained at anelevated pressure until released by action of the valve.

Compositions for buccal or sublingual administration are, for example,tablets, lozenges and pastilles, in which the substance or the prodrugis formulated with a carrier such as sugar and acacia, tragacanth, orgelatin and glycerol. Compositions for rectal administration aresuitably in the form of suppositories containing a suppository base suchas cocoa butter. Compositions for transdermal application are forexample ointments, gels and transdermal patches.

The compositions are preferably in unit dosage form such as a tablet,capsule or ampoule. Each dosage unit for oral administration willnormally contain from 1 to 100 mg (and for parenteral administrationpreferably from 0.1 to 25 mg) of a substance used according to theinvention or a prodrug therefor, calculated as the free activesubstance.

The physiologically acceptable substances or prodrugs are normallyadministered in a daily dosage of between 1 mg and 500 mg for a adultperson, usually been 10 mg and 400 mg, such as between 10 mg and 250 mgorally or an intravenous, subcutaneous or intramuscular dose of between0.1 mg and 100 mg, preferably between 0.1 and 50 mg, such as between 1mg and 25 mg of the substance. The substance or prodrug is preferablyadministered 1 to 4 times daily. As mentioned above, the administrationis normally aimed at maintaining a therapeutically effective serumconcentration of the substance for at least one month, preferably atleast two months or at least three months. Controlled release typecompositions will often be suitable for maintaining an effective serumconcentration with a small number of daily unit dosages.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the model for the development of tension-type headache.

Abbreviations; V: Trigeminal nerve, C2 and C3 Second and third cervicalsegment of the spinda cord. PAG: Periaquaductal grey, DRN: Dorsal raphenuclei, on-cells; cells in ventromedial medulla, which activate painpathways, for instance by reducing the threshold in the tail flick test.C: C fibers. Ad: A-d-fibers. Ab: Ab-flbers.

FIGS. 2(A and B) depicts stimulus-response functions in trapeziusmuscle.

Stimulus-response functions for pressure versus pain in the trapeziusmuscle in 40 patients with chronic tension-type headache (dots) and in40 control subjects (triangles)(mean±SE). Patients were significantlymore tender than controls. P=0.002. In patients, the stimulus-responsefunction was approximately linear with a slope (b)=0.50±0.04 mTNU,P=0.00004 (FIG. 2A). In contrast pain intensities increased in apositively accelerating fashion with increasing pressure intensities incontrols, a relation that was well described by a power function. Thiswas demonstrated by obtaining an approximately linear relation betweenpressure and pain in a double logarithmic plot, b=3.8±0.61 logmm/logU,P=0.002 (FIG. 2B).

FIGS. 3(A and B) depicts stimulus-response functions in temporal muscle.

Stimulus-response functions for pressure versus pain in the temporalmuscle in 40 patients (dots) and in 40 controls (triangles)(mean±SE).Patients were slighty more tender than controls, but the difference wasnot A statistically significant, P=0.42. In both groups, painintensities increased in a positively accelerating fashion withincreasing pressure intensities. (FIG. 3A) This was demonstrated byobtaining approximately linear relations between pressure and pain in adouble logarithmic plot: patients b=3.0±0.36 logmtn/logU, P=0.0002;controls b=6.7±0.36 logrmrn/ogU, P=0.00001 (FIG. 3B).

FIGS. 4(A and B) depicts stimulus-response functions in trapeziusmuscle. Stimulus-response functions for pressure versus pain in thetrapezius muscle in the 20 most tender patients (diamonds) and in the 20least tender patients (squares)(mean±SE). In the most tender patients,the stimulus-response function was linear, b=0.69±0.03 mm/U, P<0.00001.In contrast, pain intensities increased in a positively acceleratingfashion with increasing pressure intensities in the least tenderpatients. (FIG. 4A) This was demonstrated by obtaining a linear relationbet veen pressure and pain in a double logarithmic plot, b=4.0±0.18logmm/logU, P<0.00001 (FIG. 4B).

FIG. 5 shows Total Tenderness Scores in patients.

The Total Tenderness Scores (TTS) in patients outside and during aheadache episode and in controls. Median values are given (*** indicatep<10⁻⁵ and ** indicate p=0.01, Wilcoxon's test).

FIG. 6 shows Pressure Pain Thresholds (PPTO) and Pressure PainTolerances (PPTO) in patients.

Pressure Pain Thresholds (PPDT) and Pressure Pain Tolerances (PPTO) inpatients outside (closed bars) and during a headache episode(open bars).Mcan values of left and right side are given in kPa with SD as verticalbars (* indicate p<0.05. Wilcoxon's test).

FIG. 7 slows thermal thresholds in the hands and temporal (Temp) regionsof patients.

Thermal thresholds in the hands and temporal (Temp) regions of patientsoutside (closed bars) and during a headache episode (open bars). WDindicate warmth detection, HPD heat pain detection and HPTO heat paintolerance thresholds. Mean values of left and right side are given in °C. with SD as vertical bars (* indicate p<0.05, Wilcoxon's test).

FIGS. 8(A and B) depicts EMG-amplitude levels from the temporal andtrapezius muscles of patients. EMG-amplitude levels from the temporaland trapezius muscles of patients outside (closed bars) and during aheadache episode (open bars). FIG. 8A indicates the resting conditionand FIG. 8B the maximal voluntary contraction Mean values of left andright side are given in uV with SD as vertical bars.

FIG. 9 depicts pain intensities in patients and controls.

Pain intensities in those patients (filled circles) and controls (opencircles) who developed tension-type headache after a 30 minutessustained clenching procedure. The ordinate indicates the mean painintensity in mm as recorded on a 100 mm visual analogue scale. Theabscissa indicates the time after the clenching procedure (* p<0.05,Mann-Whitney's test)

FIG. 10 shows Total Tenderness Scores (TTS) in patients and in controls.

Total Tenderness Scores(TTS) in patients and in controls before and 90minutes after experimental tooth clenching with respect to developmentof headache. Median values vital quartiles are given. (** indicatep<0.01, *** p<0.001, Wilcoxon's test).

FIGS. 11(A and B) shows Pressure Pain Detection Thresholds and PressurePain Tolerances in patients and controls.

FIG. 11A shows the Pressure Pain Detection Thresholds and FIG. 11B thePressure Pain Tolerances from fingers (F), temporal (T) and parietal (P)regions from patients and controls before (filled bars) and a forclenching (open bars) with respect to development of headache Meanvalues of right and left side with SD are given in kPa. (* indicatep<0.05, ** p<0.01, Wilcoxon's test).

FIG. 12 shows thermal thresholds in the temporal region of patients andcontrols.

Thermal thresholds in the temporal region of patients and controlsbefore (filled bars) and after clenching (open bars) with respect toheadache development. WI) indicate warmth detection, PD heat paindetection and PTO heat pain tolerance. Mean values of right and leftside with SD are given in ° C.

FIGS. 13(A and B) shows EMG-amplitudes in temporal and trapezius musclesof patients and controls. FIG. 13A shows the EMG-amplitudes (Root MeanSquare-values) during resting condition and FIG. 13B during the maximalvoluntary contraction in temporal (temp) and trapezius (trap) musclesfrom patients and controls before (filled bars) and after clenching(open bars) Keith respect to headache development. Mean values of leftand right side with SD are given in uV (* indicate p<0.05, ** p<0.01 and*** p<0.001 Wilcoxon's test). FIG. 14 shows changes in pain intensityafter treatment

Post infusion chances in pain intensity (VAS) relative to pretreatmentpain intensity in 16 patients with chronic pain. L-NMMA reduced painsignificantly more than placebo (p=0.007).

FIG. 15 shows Pressure Pain Thresholds (PPDT) and Pressure PainTolerances (PPTO) in patients with chronic tension-type headacheassociated with muscular disorders (MUS) (filled bars) or unassociatedwith such disorders (non-MUS) (open bars). Mean values from the fingers,temporal (Temp) and Parietal (Par) regions are given in kPa with SE asvertical bars (*** indicate p<0.001, * indicate p=0.04).

FIG. 16 shows Pressure Pain Thresholds (PPDT) and Pressure PainTolerances (PPTO) in patients with episodic tension-type headacheassociated with muscular disorders (MUS) (filled bars) or unassociatedwith such disorders (non-MUS) (open bars). Mean values from fingers,temporal (Temp) and Parietal (Par) regions are given in kPa with SE asvertical bars. No significant differences were detected.

FIG. 17 shows the percentage of change in muscle hardness. Musclehardness was significantly more reduced following treatment with L-NMMA(dots) than with placebo (triangles) in patients with chronic myofascialpain. * denotes p<0.05 compared with baseline (time=0). The plotsrepresent mean scores.

FIG. 18 shows the percentage of change in Total Tenderness Scoring(TTS). The TTS tended to be reduced following treatment with L-NMMA(dots) compared with placebo (triangles) (p=0.11). Within eachtreatment, the TTS was significantly reduced at 60 and 120 minutes afterstart of the infusion of L-NMMA. while there was no significant changesat any time after treatment with placebo. ** denotes p<0.01 comparedwith baseline (time=0). The plots represent mean scores.

FIG. 19 shows the percentage of change from baseline pain intensity on a100 mm Visual Analog Scale. The pain intensity was significantly morereduced during treatment with L-NMMA (dots) than with placebo(triangles) (p=0.006). * denotes p<0.05 compared with baseline (time=0).The plots represent mean scores (copyright from Lancet).

EXAMPLE 1 Experimental Evidence For Central Sensitization in ChronicMyofascial Pain

The study was performed in order to investigate the pathophysiology ofmyofascial tenderness which has consistently been reported to beincreased in patients with tension-type headache (Lous and Olesen 1982;Langemark and Olesen 1987, Jensen et al. 1993b). Recently, it wassuggested that myofascial tenderness may be the result of a loweredpressure pain threshold, a stronger response to pressures in the noxiousrange (as illustrated by a steeper stimulus-response function) or acombination of both (Jensen 1990b). The aim of the study therefore wasto investigate the stimulus-response function for pressure versus painin patients with tension-type headache. The methods and the results ofthe study will be described in the following.

Materials and Methods

TABLE III Clinical data on headache patients and controls PatientsControls Number 40 40 Sex (females/males) 25/15 25/15 Age, years 40.039.8 (18-60) (18-60) Frequency of TH 24.6 <1 days/4 weeks (16-28)

Patients and Controls

Forty patients with chronic tension-type headache diagnosed according tothe criteria of the International Headache Society (1988) were examinedduring a typical episode of tension-type headache (Table III), Sevenpatients with coexisting infrequent migraine (<one day/month) wereaccepted. The patients were recruited from the out-patient headacheclinic at Glostrup Hospital without respect to presence or absence ofmyofascial tenderness. All patients underwent a general physical and aneurological examination and completed a diagnostic headache diary(Russell et al. 1992) during a 4-week run-in period. The patients werenot allowed to take analgesics on the day of examination. Patientssuffering from serious somatic or psychiatric diseases and abusers ofanalgesics were excluded. Forty healthy, age- and sex-matched volunteersserved as controls. Only controls who did not have a headache on the dayof examination and had less than 12 days with headache a year were used.All subjects gave written informed consent to participate in the study,which was approved by the local ethics committee.

Apparatus

A palpometer (Bendtsen et al. 1994) was used to investigate thestimulus-response function for pressure versus pain. The palpometerconsists of a Force Sensing Resistor™ (FSR) connected to a meter, aprinciple first described by Atkins et al. (Atkins et al. 1992). The FSRis a commercially available polymer film device, which exhibits adecreasing electrical resistance with increasing force applied to thedevice. If the force is concentrated on a small area the resistance isfurther decreased, i.e. the properties of the FSR lies somewhere betweena force transducer and a pressure transducer. The FSR is 0.33 lnm thickand circular with a diameter of 10 mm. The FSR is attached with thinadhesive tape (Microporc®) to the tip of the palpating finger. The forceapplied to the FSR is displayed on the meter scale, which is dividedinto arbitrary units from 60 to 200 arbitrary units (U). To improve thereadability of the meter, the readout is filtered using a low-passfilter. The relation between the forces applied to the plastic film andthe palpometer output is linear in the range from 80 to 200U (Bendtsenet al. 1994). This range is equivalent to a force range from 235 gm to1550 gm. The intra- and inter-observer variations for recordings ofpressure intensity have previously found to be 3.1% and 7.2%,respectively (Bendtsen et al. 1994). Detailed information on thepalpometer has been published earlier (Bendtsen et al. 1994).

Methods

The examination was performed in a standardized manner by the sameinvestigator, a trained technician (HA), throughout the whole study. Thesubjects were examined sitting in a dental chair with headrest.

Total Tenderness

Tenderness of specified pericranial regions was recorded according tothe Total Tenderness Scoring system. which has previously proved to bereliable (Bendtsen et al. 1995a). Five pairs of muscles (masseter,temporal, frontal, sternocleidomastoid and trapezius muscles) and threepairs of tendon insertions (coronoid and mastoid processes and neckmuscle insertions) were palpated. Palpation was performed with smallrotating movements of the observer's second and third fingers. Pressurewas sustained for 4-5 seconds. Prior to the study, the palpometer wasused to train the observer to exert a palpation pressure of moderateintensity (140 U). The tenderness was scored on a 4-point (0-3) scale asfollows: 0 denial of tenderness, no visible reaction, 1=verbal report ofdiscomfort or mild pain, no visible reaction; 2=verbal report ofmoderate pain, with or without visible reaction; 3=verbal report ofmarked pain and visible expression of discomfort. The values from leftand right sides were summed to a Total Tenderness Score (maximumpossible score=48).

Stimulus-response Functions

Stimulus-response functions for pressure versus pain were recordedduring pressure-controlled palpation. i.e. palpation with controlledpressure intensity by means of the palpometer. Pressure-controlledpalpation has previously proved to be a reliable method of tendernessrecording (Bendtsen et al. 1995a). Palpation was performed with smallrotating movements of the observer's second finger. Pressure wassustained for 4;5 seconds. The subjects were palpated at the trapeziusand temporal muscles at the non-dominant side. These muscles havepreviously been found to represent a highly tender and a largely normalmuscle respectively in patients with tension-type headache (Jensen etal. 1993b). Palpation was performed with seven different pressureintensities chosen in random order in the range from 80 to 200 U. Ateach pressure intensity the subject indicated the corresponding painintensity on a visual analogue scale blinded for the observer. Thevisual analogue scale consisted of a 100-mm line with endpointsdesignated “no pain” and “unbearable pain”. The degree of tendernesselicited in each subject was calculated as the area under thestimulus-response curve (AUC) according to the trapezium rule (Matthewset al. 1990).

Statistics

Results are presented as mean±SE. Data were analyzed with Mann-Whitney'stest and simple linear regression. Five percent was accepted as level ofsignificance.

Results

Total Tenderness

The Total Tenderness Score in patients was 17.7±1.7 and significantlyhigher than 3.4±0.53 in controls, P<0.00001.

Stimulus-response Functions

The stimulus-response functions for pressure versus pain in thetrapezius muscle in patients and in controls are shown in FIG. 2.Calculating the area under the stimulus-response functions revealed thatpatients were significantly more tender (AUC=3370±423 mnmU than controls(AUC=1693±269 mmn n), P=0.002. In controls, pain intensities increasedin a positively accelerating fashion with increasing pressureintensities. The stimulus-response function was well described by apower function. This was demonstrated by obtaining an approximatelylinear relation between pressure and pain in a double logarithmic plot,slope (b)=35 0.61 logmm/logU, P=0.002 (FIG. 2B). In contrast, thestimulus-response function was approximately linear in patients,b=0.50±0.04 mm/U, P=0.00004. Thus, the stimulus-response functions incontrols and in patients were qualitatively different.

The stimulus-response functions for pressure versus pain in the temporalmuscle are shown in FIG. 3. Patients were slightly more tender(AUC=2139±327 mmU) than controls (AUC=1722±257 mmU), but the differencewas not statistically significant, P=0.42. In controls, pain intensitiesincreased in a positively accelerating fashion with increasing pressureintensities. In a double logarithmic plot the relation between pressureand pain was linear, b=6.7±0.36 logmm/logU, P=0.00001 (FIG. 3B). Inpatients, pain intensities increased in a positively acceleratingfashion with increasing pressure intensities. However, the curve wasirregular partly resembling a linear function. The regression functionwas approximately linear in a double logarithmic plot b=3.0±0.36logmm/logU, P=0.0002 (FIG. 3B).

To explore whether the abnormal stimulus-response function in thetrapezius muscle was related to the increased tenderness or to thediagnosis of tension-type headache, the patients were subgrouped on thebasis of their degree of tenderness. The stimulus-response functions forthe 20 most tender patients (AUC=5359±538 mmU) and for the 20 leasttender patients (AUC=1381±176 mmU) are shown in FIG. 4. In the 20 mosttender patients, the stimulus-response function was linear, b=0.69±0.03mun/U, P<0.00001. In contrast, pain intensities increased in apositively accelerating fashion with increasing pressure intensities inthe 20 least tender patients. In a double logarithmic plot the relationbetween pressure and pain was linear, b=4.0±0.18 logmm/logU, P<0.00001(because none of the patients reported any pain at the lowest stimulusintensity U=80), a value of 1 mm was added to all pain intensities inorder to perform this analysis)(FIG. 4B).

Discussion

Possible physiological mechanisms leading to myofascial pain include: a)sensitization of peripheral myofascial nociceptors, b) sensitization ofsecond order neurons at the spinal/trigeminal level, c) sensitization ofsupraspinal neurons, and d) decreased antinociceptive activity fromsupraspinal structures. These mechanisms may be investigated by relatingthe intensity of mechanical pressure applied to deep tissues to theresponse recorded from sensory neurons. Such studies on animal modelshave provided important information on deep tissue pain (Ness andGebhart 1987; Cervero and Sann 1989; Yu and Mense 1990, Jänig andKoltzenburg 1991), but till now the relation between pressure and painhas not been investigated in patients with chronic myofascial pain.

Previously the stimulus-response function for pressure versus pain hadbeen studied in 30 subjects with tender pericranial muscles (15 headachepatients and 15 volunteers) (Bendtsen et al. 1995a). In the trapeziusmuscle, an approximately linear stimulus-response function virtuallyidentical to the one recorded in patients in the present study wasfound. The finding of almost identical results in two different butcomparable populations obtained by two different observers, indicatesthat the employed method for recording of stimulus-response functions isreliable.

Before the present investigation, the stimulus-response function innormal muscle was expected by the inventors to be qualitatively similarto the stimulus-response function in tender muscle, i.e. linear, butwith a less steep slope or with a parallel shift to die right aslipothesized by Jensen (Jensen 1990). Surprisingly, the relation betweenpalpation pressure and pain in normal muscle and in highly tender musclediffered markedly. In the trapezius and temporal muscles of controls,pain intensities increased in a positively accelerating fashion withincreasing pressure intensities, a relation that was well described by apower function. The same was found in patients in the temporal musclewhich was only slightly to moderately tender. The patients weresubgrouped on the basis of their degree of tenderness, thestimulus-response function was linear in the most tender patients, whileit was well described by a power function in the least tender patients.Thus, the stimulus-response function becomes increasingly linear withincreasing degrees of tenderness and the qualitatively changedstimulus-response function is related to actual tenderness and not tothe diagnosis of tension-type headache. The possibility that the linearstimulus-response function was due to a shift to the left or the normalstimulus-response function such that the patients were on the steep partof the curve already at low pressures can be excluded. If so, thepatients would have been much more tender than controls also at thelowest stimulus-intensities, which was not the case.

The present finding of a qualitatively altered response to nociceptorstimulation in tender muscle demonstrates for the first time thatmyofascial pain has a physiological basis and that myofascial pain, atleast in part, is caused by qualitative changes in the processing ofsensory information. These changes may be located to peripheral nerveendings, to the spinal cord or to higher order neurons.

Spinal dorsal horn neurons that receive input from deep myofascialtissues can be classified as high-threshold mechanosensitive (HTM)neurons requiring noxious intensities of stimulation for activation andas low-threshold mechanosenisitive (LTM) neurons, which are activated byinnocuous stimuli (Mense 1993). Yu and Mense (Yu and Mense) 1990) haveshown that HTM dorsal horn neurons have a positively acceleratingstimulus-response function, whereas the stimulus-response function ofLTM neurons is approximately linear. This indicates that the linearstimulus-response function in tender human muscle may be caused byactivity in LTM afferents. LTM afferents do not normally mediate pain,but strong input from peripheral nociceptors can remodel the circuitryof the dorsal horn by unmasking previously ineffective synapses and byforming novel synaptic contacts between LTM afferents and dorsal hornneurons that normally receive input from LTM afferents (Wall 1977; Walland Woolf 1984; Cervero and Jänig 1992;Hu et al. 1992; Woolf et al.1992; Mense 1993; McMahon et al. 1993; Mayer and Gebhart 1994;Hoheiselet al. 1994). In this way LTM afferents can mediate pain (Woolf andThompson 1991). While the above-mentioned studies have been performed onanimal models (Torcbjörk et al. 1992). Torebjörk et al. havedemonstrated similar changes in the central processing of inputs fromLTM afferents in humans following intradermal injection of capsaicin. Ittherefore seems probable that the present findings ca be explained bychanges in neuronal behavior at the spinal/trigeminal level. Support forthis explanation was provided by a simultaneous investigation of painthresholds in the same subjects by means of an electronic pressurealgometer. Patients had significantly lower pressure pain detection andtolerance thresholds in fingers than controls (Bendtsen et al. 1996a).This indicates that the pain perception is centrally disturbed. Adecrease of the supraspinal descending inhibition probably does notexplain the present findings, because it has been reported that thedescending inhibition acts via a parallel shift or via a decreased slopeof the stimulus-response curve (Ness and Gebhart 1987; Yu and Mense1990), while it does not change the shape of the stimulus-responsecurve. Sensitization of normally active peripheral nociceptors wouldprobably induce a quantitative rather than a qualitative change of thestimulus-response curve (Koltzenburg et al. 1992).

The results thus demonstrate for the first time that nociceptiveprocesses are qualitatively altered in patients with chronictension-type headache, and that the central nervous system is sensitizedat the spinal/trigeminal level in these patients.

Recent studies from the present inventors indicating that the centralsensitization is induced by prolonged muscle pain

As mentioned above, the information obtained from basic pain researchsuggests that the central sensitization in chronic tension-type headacheis induced and probably maintained by prolonged noxious input from theperiphery. Prolonged muscle pain is, in particular, likely to inducecentral sensitization, because input from muscle nociceptors is moreeffective in inducing prolonged changes in the behavior of dorsal hornneurons than is input from cutanceous nociceptors (Wall and Woolf 1984).Recent research from the present inventors does for the first timesupport that there is a clear relation between central pain sensitivityand the increased muscle pain in patients with tension-type headache,and that the increased central pain sensitivity is induced by theincreased muscle pain. Thus, it has recently been demonstrated thatpatients with chronic tension-type headache have decreased painthresholds to various types of stimuli both at cephalic and atextra-cephalic locations (Bendtsen et al. 1996b), indicating a state ofcentral hypersensitivity, and that there is a significant correlationbetween cephalic as well as extra-cephalic pain thresholds and the totalpericranial tenderness recorded by manual palpation (Bendtsen et al.1996a). These findings demonstrate that there is a close relationshipbetween the increased pericranial tenderness and the centralhypersensitivity in chronic tension-type headache, but it does notreveal the cause and effect relationship between these abnormalities.However, since it is known that patients with episodic tension-typeheadache have normal pain thresholds (Jensen et al. 1993b) and thatchronic tension-type headache usually evolves from the episodic form(Langemark et al. 1988), and since experimentally induced tenderness ofmasticatory muscles precedes the induced headache by several hours inpatients with tension-type headache (Jensen and Olesen 1996), it is mostlikely that increased myofascial tenderness precedes centralhypersensitivity.

EXAMPLE 2 Mechanisms of Spontaneous Tension-type Headaches

An analysis of tenderness, pain thresholds and EMG

Pericranial muscle tenderness, EMG-levels and thermal and mechanicalpain thresholds were studied in 28 patients with tension-type headacheand in 30 healthy controls. Each patient was studied during as well asoutside a spontaneous episode of tension-tape headache. Outside ofheadache muscle tenderness and EMG-levels were significantly increasedcompared to values in controls subjects, while mechanical and thermalpain thresholds were largely normal. During headache muscle tendernessevaluated by blinded manual palpation increased significantly, whilepressure pain thresholds remained normal and pressure pain tolerancesdecreased. Thermal pain detection and tolerance threshold decreasedsignificantly in the temporal region, but remained normal in the hand.EMG-levels were unchanged during headache. The findings indicate thatone of the primary sources of pain in tension-type headache may be alocal and reversible sensitization of nociceptors in the pericranialmuscles. In addition, a segmental central sensitization may contributeto the pain in frequent sufferers of tension-type headache. The presentstudy, for the first time, examines the same patients both duringheadache and outside of a headache episode with the following tests;EMG, pericranial palpation, mechanical and thermal pain thresholds. Theaim was to analyze the relative importance of central and peripheralnociceptive factors.

Subjects and Methods

Subjects

Twenty eight patients, 11 males and 17 females, with frequent episodicor chronic tension-type headache fulfilling the IHS-criteria (HCCIHS1988) were included (Table IV). The patients were recruited from theout-patient headache clinic at Gentofte Hospital, Denmark. 9 patientswith frequent episodic tension-Cape headache (ETH)³ 8 days per month and19 patients with chronic, but not daily, tension-type headache (CTM)(HCCIHS 1988) were included. The reason for this selection was thatpatients had to have frequent headaches as well as frequent days withoutheadache in order to be studied in both states. Further inclusioncriteria were frequent headaches during at least one year and an agebetween 18 and 70 years. The exclusion criteria were: Daily headache,migraine more than 1 day per month, cluster headache or trigeminalneuralgia, other neurological, somatic or psychiatric disorders,concurrent ingestion of major medications including migraineprophylactics, any form of drug abuse or dependency including largeamounts of plain analgesics. A diagnostic headache diary had to befilled out during a 4 week run-in period to ensure that patientsfulfilled the inclusion criteria. A complete physical and neurologicalexamination was performed before entry. Thirty age- and sex-matchedhealthy subjects Without tension-type headache (<14 days Rear) were usedas controls (Table IV). Informed consent was obtained and the study wasapproved by the local ethical committee.

Methods

The patients were examined randomly during and outside a typical episodeof tension-type headache. The intensity of the headache was recordedinitially on a 100 mm Visual Analogue Scale (VAS), where 0 indicated nopain at all and 100 mm indicated the worst imaginable pain. Examinationswere separated be at least one week and performed at the same time ofthe day in order to eliminate diurnal variations. Patients were notallowed to take any medication on the days of examination. Healthycontrols were investigated once.

Examination

The examination was performed in a standardized fashion by the sameinvestigator, a trained technician (LM), throughout the whole study. Thetechnician was blinded to the subjects' headache history and presence orabsence of a possible muscular factor. Before measuring pain thresholdseach individual was carefully instructed to apply the sameinterpretation of ‘painful’ throughout the study. Initial test sessionswere applied to all subjects in order to familiarize them with the testconditions.

Palpation Method

Pericranial tenderness was evaluated by palpation of 9 pairs of musclesand tendon insertions in a standardized way. Each patient was examinedby the technician and the physician in random order. Tenderness wasscored at each location according to a four point scale from 0 to 3, andscores from all sites were summated. The maximally possible score wasthus 54 points. This Total Tenderness Score system (TTS) has previouslyproved to be reliable (Bendtsen et al. 1996).

Pressure Pain Threshold

The mechanical pain thresholds and tolerances were evaluated bilaterallyon the distal dorsal part of the second finger. Similarly, 2 craniallocations, one with interposed muscle, the anterior part of the temporalmuscle (temp) and one without interposed muscle, the parietal region(par) were examined (Petersen et al. 1992). A standardized andpreviously evaluated method was applied using an electronic pressurealgometer (Somedic AB, Sweden) with a 0.79 cm. circular probe (Jensen etal. 1986, Brennum et al. 1989). The Pressure Pain Detection Threshold(PPDT) was defined as the threshold, where the pressure sensation becamepainful, whereas the Pressure Pain Tolerance (PPTO) was the thresholdwhere the patient would no longer tolerate the pain (Petersen et al.1992). By pressing a hand-held button the subjects indicated that thepain threshold was reached and the pressure was immediately released. Ifpatients did not activate the button, the experiment was terminated whenreaching 800 kPa in the cranial region and 1500 kPa in the fingers. Eachthreshold was calculated as the median value of 3 consecutiverecordings.

Thermal Thresholds

Thermal thresholds were evaluated with a computerized version of theThermotest (Somedic AB, Sweden)(Fruhstorfer et al. 1976). The thermodeconsisted of series-coupled Peltier elements and measured 25×50 mm. Twolocations, the thenar region of the hand and the anterior part of thetemple were examined bilaterally. Three parameters were recorded in eachregion i.e. the Warm Detection (WD) defined as the lowest temperaturedetected as swarm, the Heat Pain Detection (HPD) defined as thetemperature where the heat sensation became painful, and the Heat PainTolerance (HPTO) defined as the highest temperature tolerated (Langemarket al. 1989, Jamal et al. 1985). A baseline temperature of 32° C. and a1.0° C./sec rate of temperature change was used (Langemark et al. 1989).Heat stimulation was terminated when reaching 52° C. if the patients hadnot responded before. By pressing a hand-held button the subjectsindicated, when the thresholds were reached. The thermode wasimmediately removed from the area, the exact value was recorded in thecomputer and the stimulator returned to baseline. Each threshold wascalculated as the average of 5 determinations performed with intervalsof 10-15 seconds.

Electromyography

A standardized, previously described method was used (Jensen et al.1993a, Jensen et al. 1994). The EMG signals from the temporal andtrapezius muscles were recorded bilaterally using a 4-channelselectromyograph (Counterpoint, Dantec, Copenhagen). Data were collectedduring 2 conditions i.e. resting in the supine position in 20 one secondperiods interrupted by 5 second interval and during maximal voluntarycontraction (MVC). The MVC lasted a maximum of 5 seconds and wasrepeated 5-6 times with 30 second intervals. MVC recording sessionslasting one second were analyzed and the highest value of Root MeanSquare (RMS) of the EMG was selected (Jensen et al. 1993a, Jensen et al.1994). The power spectrum of each of the 1 second measurement sessionswas calculated for the frequency range 0 to 1 kHz and Mean Frequency wasextracted (Jensen et al. 1993a).

STATISTICS

Wilcoxons rank sum test (Wilc.) was used to compare paired data fromheadache subjects. Mann-Whitneys test (M-W.) was used to compare databetween controls and patients. Mean values of right and left sidedobservations are presented. Five percent level of significance was used.

RESULTS

Subjects

All the included patients ad healthy controls completed the study. Therewere no significant differences in age and sex-distribution betweenhealthy subjects and patients (Table IV).

Headache

The headaches examined fulfilled the diagnostic criteria fortension-type headache (HCCIHS 1988). Seventy one percent (20/28) had abilateral headache, whereas 29%(8/28) had a unilateral headache. Themedian VAS score was initially 35 mm (range 17-75 mm).

Variation Between Observers

The Total Tenderness Scores(TTS) as recorded by the 2 observers (LH, RJ)at the initial examination were comparable in patients (Wilc.p=0.38) andin healthy controls (Wilc.p=0.27).

Side to Side Relation

The side to side variations were tested in patients as well as incontrols, and results corresponded to previous methodological studies(Petersen et al. 1992, Jensen et al. 1986, Jamal et al. 1985, Jensen etal. 1993a).

Relation Between Controls and Patients Free of Headache

Tenderness

Median TTS in TR patients free of headache *ins 13 and significantlyhigher than 4 in healthy controls (M-W.p<10⁻⁵) (FIG. 5).

Pressure Pain Thresholds

Pressure Pain Detection Thresholds and Pain Tolerance Thresholds inpatients were not significantly different from those in healthy controlsin any of the examined regions (Table V).

Thermal Thresholds

The warm detection threshold, the heat pain detection and tolerancethresholds in the hands did not differ between patients and controls. Inthe temporal regions of headache free patients the warn detection (WD)and heat pain thresholds (HPD) were increased compared to healthycontrols (Table VI) (M-W. WD:p<0.001;HPD:p=0.047). The heat paintolerances were similar in the 2 groups (Table VI).

EMG

During rest amplitude-levels were higher in patients in the headachefree condition as compared to healthy controls(M-W.m.temp:p<0.001;m.trap p=0.016). No other significant differences ortendencies were detected (Table VII).

Relation to the Headache State

Tenderness

The total tenderness score increased from 13 (range 0-29) outside ofheadache to 16 (range 1-34) during headache (Wilc.p<0.01) (FIG. 5)

Pressure Pain Thresholds

No significant differences in pressure pain detection thresholds werefound when results during headache were compared to the headache freecondition. Pressure pain tolerances in the parietal regions decreasedsignificantly during the headache (Wilc.p=0.03), whereas the pressurepain tolerances from other locations were unaffected (FIG. 6).

Thermal Thresholds

Heat pain detection (Wilc.p=0.011) and tolerances (Wilc.p=0.016) werelower in the temporal region during headache as compared to the headachefrom condition. No differences were seen in the hand (FIG. 7).

EMG

No significant variations appeared when EMG parameters during theheadache episode were compared to the headache free condition (FIG.8A+B).

Discussion

Comparison of headache-free patients and control subjects

Myofascial tissue has been considered an important source of nociceptionin tension-type headache by some investigators (Travell et al. 1983,Drummond et al. 1987), whereas others favor alterations in central painprocessing resulting in a state of hypersensitivity to incoming stimulifrom myofascial and other cephalic tissues (Schoenen et al. 1991a,Schoenen et al. 1991b). Previous findings of increased cranial andperipheral sensitivity in patients with chronic tension-type headachesupport such central mechanisms Langemark et al. 1989, Schoenen et al.1991b). However, normal cranial pressure pain thresholds have recentlybeen described in subjects with chronic tension-type headache from ageneral population (Jenseu et al. 1993b) and in patients with episodictension-type headache from headache clinics (Goebel et al. 1992, Boviinet al. 1992) Comparing groups of headache patients to normal controlsinvolves many confounding factors. These are greatly diminished instudies comparing the headache state and the non-headache state in thesame individuals. The same patients were studied both during and outsideof headache. The headache mechanisms were analyzed by means of EMG,pericranial palpation, thermal and mechanical pain sensitivity.

The present study confirms that pericranial muscles of these patientsoutside of headache are more tender than in healthy subjects (Jensen etal. 1993,Hatch et al. 1992, Langemark et al. 1987). More importantly itis demonstrated, for the first time, that tenderness increases duringthe headache phase. Are these findings due to central or peripheralhypersensitivity Normal pressure pain thresholds and pressure paintolerances outside headache both in the cranial region and in the landsindicates that central pain perception is not generally affected inthese patients. The warm detection and heat pain detection thresholdswere increased, not decreased, in the temporal region and normal in thehands. Thus, decreased sensitivity to noxious heat can be due to eithera local factor in the skin which decreases the cutaneous receptorsensitivity or central factors inhibiting the incoming stimuli. Nostudies have addressed this issue before and the finding needs furtherclarification. Higher EMG-amplitude values during rest were recorded inheadache free patients as compared to normal controls. These findingscorrespond Faith a recent population study where amplitude levels fromthe temporal and the frontal muscles were increased in subjects withchronic tension-type headache (Jensen et al. 1994). These findingsindicate that the muscles are insufficiently relaxed. Whether this iscausative or secondary to the headache has been much debated, but lackof correlation to the pain state(see below) indicates that it may be asecondary characteristic. In the study presented in example 3 it isdescribed that sustained tooth clenching nay be an initiating event oftension-type headache, but the present results suggests that othermechanisms are responsible for maintaining it.

Relation to the Headache State

During headache pericranial tenderness increased, indicating peripheralor central sensitization of myofascial nociception (Jensen et al 1990).EMG-levels were unchanged during headache which makes it unlikely thatpain elicited activity in pericranial muscles can explain the increasedtenderness. Pressure pain thresholds were unaffected by the headachestate whereas thermal pain detection and tolerance thresholds decreasedselectively in the temporal region indicating that the actual headacheepisode may be associated with a segmental central sensitization and/ora decreased antinociception. A more generally defective central painmodulation, as previously suggested (Schoenen et a. 1991a), is lesslikely, because pressure pain thresholds and tolerances in the handswere completely normal. A possible segmental disturbance at thespinal/trigeminal level may be transient and reversible since paintolerances were normal outside of headache. The results are thus in linewith the recent experimental studies by Hu et al.(Hu et al. 1992). Inthese important studies deep craniofacial muscle afferents werestimulated and prolonged facilitatory effects in the trigeminalnociceptive brain-stem neurons of anaesthetized rats were induced. Thesefindings were supported by the recent findings that experimentalmyositis induces functional reorganization of the rat dorsal horn(Hoheisel et al. 1994). A reversible expansion of the cutaneousmechanoreceptive field was noted by Hu et al. and the spontaneousactivity in cutaneous afferents was increased (Hu et al. 1992) incorrespondence with previous studies (Coderre et al. 1993, Heppelmann etal. 1987). It is also known that input from deep myofascial tissue ismore effective in inducing central sensitization than cutaneous input(Wall et al. 1984, Yu et al. 1993).

The decreased pain tolerances during headache in the present study mayindicate a central hyperalgesia. As pain tolerances were normal outsideof headache, the central changes are probably reversibly linked to theheadache pain in the episodic form, whereas a more frequent activationmay induce a permanent pain condition, i.e. the chronic form. Thecascade of increased nociceptive activity from deep myofascial tissuesmay induce secondary changes such as plasticity and sensitization in thespinal dorsa horn/trigeminal nucleus (Hu et al. 1992, Hogeisel et al.1994, Coderre et al. 1993, Heppelmann et al. 1987). The centralnociceptive modulation and perception are thereby disturbed resulting ina prolonged hyperalgesia, which may persist despite disappearance of theperipheral noxious stimulus. When the central sensitization becomessufficiently strong and widespread, the headache becomes chronic due toself perpetuating disturbances in the pain perception system.

Many of the abnormal findings in previous series of severely affectedpatients with chronic tension-type headache (Schoenen et al. 1991a,Langemark et al. 1989, Schoenen et al. 1991b) maybe a function of thepain rather than the initial causative factor. It can therefore berecommended to study mechanisms in patients with episodic tension-typeheadache. Studies comparing the pain state to the pain free state inthese patients are likely to be the most informative.

TABLE IV Clinical characteristics of the subjects studied TH patientsControls Number (n) 28 30 Males 11 12 Females 17 18 Age (years) 45 42(28-63) (23-67) Years with Th 23 —  (1-45) Frequency of TH 20 — days/28days  (8-27) Frequency of migr  8 — days/year (n = 14)  (2-11) Meanvalues with range in brackets are given

TABLE V Pressure pain thresholds in 28 headache patients free ofheadache and 30 healthy controls. Mean values of left and right side aregiven in kPa with SD in brackets. Pressure Pressure pain detection paintolerance HANDS patients 384(161) 739(271) controls 358(168) 785(289)TEMPORAL REG. patients 225(97)  366(141) controls 203(103) 387(157)PARIETAL REG. patients 339(172) 560(179) controls 317(194) 571(201) Nosignificant differences between patients and controls.

TABLE VI Thermal thresholds in 28 headache patients free of headache and30 healthy controls. Mean values of left and right side are given in °C. with SD in brackets. Warm Pain Pain Detection threshold toleranceHANDS patients 34.3(3.1) 42.3(3.1) 47.0(2.2) controls 34.4(1.2)42.4(2.7) 47.5(2.2) TEMP patients ***34.7(1.6)   *40.1(2.8)  44.1(2.0)controls 33.8(0.8) 39.1(2.7) 43.9(3.5) *p < 0.05 ***p < 0.001(Mann-Whitney's test)

TABLE VII EMG levels in 28 patients free of headache and in 30 healthycontrols. REST indicate resting conditions and MVC indicate maximalvoluntary contraction. Mean values of left and right side are given withSD in brackets. REST MVC RMS Mean F RMS Mean F (uV) (Hz) (uV) (Hz)TEMPORAL MUSCLES patients **3.1(2.4) 81(25) 164(66)  173(28) controls 2.3(0.9) 74(17) 181(101) 155(30) TRAPEZIUS MUSCLES patients  *3.6(1.2)40(10) 260(141)  88(18) controls  3.1(0.9) 41(9)  259(131)  88(16) *p <0.05 **p < 0.01 (Mann-Whitney's test)

EXAMPLE 3 Initiating Mechanisms of Experimentally Induced Tension-typeHeadache

To elucidate possible myofascial mechanisms of tension-type headache,the effect of 30 minutes of sustained tooth clenching (10% of maximalEMG-signal) was studied in 58 patients with tension-type headache and in30 age and sex matched controls. Pericranial tenderness, mechanical andthermal pain detection and tolerance thresholds and EMG levels wererecorded before and after the clenching procedure. Within 24 hours 69%of patients and 17% of controls developed a tension-type headache.Shortly after clenching, tenderness was increased in the group whosubsequently developed headache, whereas tenderness was stable in thegroup of patients who remained headache free. Mechanical pain thresholdsevaluated by pressure algometry remained unchanged in the group whichdeveloped headache, whereas thresholds increased in the group which didnot develop headache Thermal pain detection and tolerance thresholdsremained unchanged in both groups. These findings indicate that,although there may be several different mechanisms of tension-typeheadache, one of them is sustained muscle contraction. A peripheralmechanism of tension-type headache is therefore possible, whereas asecondary segmental central sensitization seems to be involved insubjects with frequent tension-type headache. Finally, the increase inpressure pain thresholds in patients who did not develop headachesuggest that clenching activated their antinociceptive system whereasthose developing headache were unable to do so.

Introduction

Tension-type headache is extremely prevalent (Rasmussen et al. 1991) andrepresents a major health problem (Rasmussen et al. 1992). Nevertheless,its pathogenic mechanisms are largely unknown (Pikoff et al. 1984,Olesen et al. 1991). Sustained involuntary muscle contraction has beensuggested as in important source of pain in tension-tape headache(Travell et al. 1983). In recent years, central mechanisms have however,been favoured (Schoenen et al. 1991a). Substantial evidence for any ofthe suggested pathogenetic mechanisms has not yet been available. Tostudy the initiating mechanisms of headache it is valuable to induce it.The time necessary to reach the laboratory males it impossible to studythe initial phase of spontaneous attacks. Furthermore, using a knownstimulus to induce headache makes it easier to analyze its mechanisms.Experimental tooth clenching has previously induced mild headaches inmigraineurs (Jensen et al. 1985) but has never been studied in subjectswith tension-type headache. In the present study tension-type headachewas induced by sustained muscle contraction in patients and controls andstudied the pre- and post-contraction phase by means or EMG, thermal andpressure pain thresholds as well as headache and tenderness scoring.

Subjects and Methods

Subjects

Fifty-eight patients with frequent episodic or chronic tension-typeheadache fulfilling the IHS-criteria (HCCIHS 1988) were included (TableVIII). Twenty eight patients had frequent episodic tension-type headache38 days with headache per month and 30 patients had chronic, but notdaily, tension-type headache (HCCIHS 1988). The reason for thisselection was that patients had to have frequent headaches as well asdays without headache in order to be studied in the latter state.Further inclusion criteria were duration of frequent tension-typeheadache in at least one year and age between 18 and 70 years. Theexclusion criteria were: daily headache, migraine more than 1 day permonth, cluster headache, trigeminal neuralgia, other neurological,systemic or psychiatric disorders, ingestion of major medicationsincluding migraine prophylactics, any form of drug abuse or dependencyas daily ergotamine or large amounts of plain analgesics. The patientswere recruited from the out-patient headache clinic at Gentofte Hospitaland complete physical and neurological examinations were done beforeentry. Thirty healthy age- and sex matched subjects (headache<14days/year) were used as controls (Table VIIH). Informed consent wasobtained and the study was approved by the local ethical committee.

Procedure

All patients had to fill in a diagnostic headache diary during a 4 weekrun-in period to ensure that patients fulfilled the inclusion criteria.All subjects, patients and controls, were told to fill out a specialdiary for at least 24 hours after the study. Patients were examined whenfree of headache and there not allowed to have taken any analgesics onthe day of examination. The EMG-parameters and pain characteristics wererecorded twice on the day of examination, immediately before and afterthe clenching procedure. A 100 mm Visual Analogue Scale (VAS), where 0mm was no pain at all and 100 mm was the worst imaginable pain was used.Recordings of pain intensity were made before, 30, 60 and 90 minutesafter the clenching procedure in the laboratory, as well as after 4, 6,and 24 hours after the clenching in the diary. All subjects wereinformed that the purpose of the study was to measure variations inmuscle tension and pain characteristics during tooth clenching. Theywere not informed of the risk of developing headache in order to avoidbias.

Examination

The examination was performed in a standardized way by the same person,a trained technician, throughout the whole study. The study was blindedas the technician was unaware of the subjects headache history, Beforerecordings of pain thresholds each individual was carefully instructedto apply the same interpretation of ‘painful’ throughout the study.Initial test sessions were applied to all subjects in order tofamiliarize them with the test conditions.

Palpation

Pericranial tenderness was evaluated by palpation of 9 pairs of musclesand tendon insertions by the technician and the physician in astandardized, randomized procedure. Tenderness was scored in eachlocation according to an ordinal scale from 0 to 3, and scores from allsites were summated. The maximum possible score was thus 54 points. ThisTotal Tenderness Score system (TTS) has previous proved to be reliable(Bendtsen et al. 1995).

Pressure Pain Thresholds

The pressure pain thresholds were evaluated bilaterally on the distaldorsal part of the second finger, and in two cranial locations, one withinterposed temporal muscle (Temp) and one without interposed muscle, theparietal region (Par). A standardized and previously evaluated methodwas applied using an electronic pressure algometer (Somedic AB, Sweden)with an 0.79 cm circular stimulation probe (Petersen et al. 1992, Jensenet al. 1986, Brennum et al. 1989). Two pain qualities were recorded, thePressure Pain Detection Threshold (PPDT) defined as the threshold, wherethe pressure sensation became painful, and the Pressure Pain Tolerance(PPTO) defined as the threshold where the patient would no lonertolerate the pain (Petersen et al. 1992). By pressing a hand held buttonthe subjects indicated that the threshold was reached, and the pressurewas released immediately. If patients did not activate the button, theexperiment was terminated when reaching 800 kPa in the cranial regionand 1500 kPa in the fingers. Each threshold as calculated as the medianvalue of 3 determinations performed with intervals of 10-1; seconds.

Thermal Pain Tthresholds

Thermal thresholds were evaluated with a computerized version of theThermotest (Somedic AB, Sweden) (Fruhstorfer et al. 1976). The thermodeconsisted of series-coupled Peltier elements and measured 25×50 mm. Thethenar region of the hand and the anterior part of the temporal regionwere examined bilaterally. Three stimulation qualities were recorded;the Warm Detection limit (WD) defined as the lowest temperature detectedas warm, the Heat Pain Detection (HPD) defined as the temperature wherethe heat sensation became painful and the Heat Pain Tolerance (HPTO)defined as the highest temperature tolerated (Jamal et al. 1985). Abaseline temperature of 32° C. and a 1.0° C./sec rate of temperaturechange was used. Heat stimulation was terminated when reaching 52° C. ifthe patients had not responded before. By pressing a hand-held buttonthe subjects indicated when the actual threshold was reached. This valuewas recorded automatically and the stimulator returned to baseline. Eachthreshold was calculated as the average of 5 determinations performedwith intervals of 10-15 seconds.

Electromyography

EMG signals from the temporal and trapezius muscles were recordedbilaterally by a 4-channels electromyograph (Counterpoint, Dantec,Copenhagen)(Jensen et al. 1993a). A standardized, previously describedmethod where the temporal and frontal muscles were investigated wereapplied (Jensen et al. 1993a). Data were collected during rest in thesupine position and during maximal voluntary contractions (MVC) (Jensenet al. 1993a). The RMS voltage was measured. Power spectrum wascalculated for the frequency range 0 to 1 kHz and Mean Frequencies MeanF) were extracted (Jensen et al. 1993a).

Provocation

After the initial recording series the subjects were instructed toclench their molar teeth and the EMG activity from the temporal muscleswas recorded. The subjects were instructed to clench their teeth at l0%of their individual MVC value and to keep this value constant for 30minutes. The subjects received visual feed back from the EMG-monitor,and were allowed 3 short (<60 sec) rests during the session. Force wasnot measured.

Statistics

The chi square test was used to test differences in headachecharacteristics between patients and controls. The sign test was used tocompare the frequency of provoked headache with the expected frequency.Wilcoxon's rank sum test (Wilc.) was used for comparing paired datawithin subjects, and Mann-Whitney's test (M-W.) was used for comparingpaired data between patients and controls. Five percent level ofsignificance was used.

Results

All the included patients and healthy controls completed the study. Nosignificant variation in age- and sex distribution between patients andcontrols appeared (Table VIII). Only two left handed subjects (Ipatient, 1 control) were included. Therefore no correction for handdominance was made.

Development of Headache

In total, 69%(40/58) of the patients and 17%(5/30) of the healthycontrols developed headache within 24 hours after tooth clenching. Thefrequency of headache among patients was significantly higher thanexpected from their usual headache frequency(p=0.016) and higher than inhealthy controls (p<0.0001). Twenty-eight percent of patients(16/58) and7% of controls(2/30) developed headache within the first hour aftertooth clenching. The median duration from clenching to development ofheadache was 1.5 hours in patients (range 0.5-20 hours) and 1.5 hours(range 0.5-6 hours) in controls. Ail headaches, in patients as well asin controls, fulfilled the diagnostic criteria for tension-type headache(n=7). The headaches were bilaterally located in 85%(34/40) of thepatients and in all controls. It was of pressing quality in allsubjects. It was not aggravated by physical activity in 85%(34/40) ofthe patients and in all the controls. No associated symptoms such asnausea, photophobia or phonophobia were reported. Initially, theheadache was very mild in both groups, but the intensity increasedduring the following hours in patients (FIG. 9). Four and 24 hours afterclenching those patients who had developed headache had significantlyhigher mean VAS-scores than those few healthy controls who had developedheadache (M-W.p=0.02) (FIG. 9). In patients, the median headacheduration was 8 hours (range 1-24 hours) but not significantly differentfrom 3 hours (range 2-24 hours)(M-W.p=0.10) in the small number ofcontrols(n=5) with headache.

Variation Between Observers

The Total Tenderness Scores (TTS) recorded by the 2 observers at theinitial examination did not differ significantly within patients(Wilc.p=0.24) nor in healthy controls (Wilc.p=0.27).

Variation Between Left and Right Sided Observations

The side to side variations were tested in patients as well as incontrols, and results corresponded to precious methodological studies(Petersen Ct al. 1992, Fruhstorfer et al. 1976, Jensen et al. 1993a,Jensen et al. 1993b). For simplicity mean values of left and right sidedobservations are presented in the following.

Relation Between Measurements in Patients and Controls Before Clenching

Tenderness

Initial median TTS in patients was 12 (range 0-29) and significantlyhigher than the median score of 4 (range 0-10) in healthy controls(M-W.p<10⁻⁷).

Pressure Pain Thresholds

Pressure Pain Detection Thresholds were increased in the temporalregions of headache patients compared with healthy controls (M-W.p=0.03)(Table IX). No significant variations or tendencies were found in theother locations (M-W.fingers p=0.98; parietal p=0.21)(Table IX).

Pressure Pain Tolerances in patients were not significantly differentfrom those in healthy controls in any of the examined regions(M-W.fingers p=0.87; temp.p=0.45; parietal p=0.69) (Table IX).

Thermal Thresholds

The warm detection threshold seas higher in the temporal regions inpatients than in healthy controls (M-W.p=0.02), while the warm detectionin the hinds was normal (M-W.p=0.26)(Table X). The heat pain detectionand tolerance thresholds were normal in both locations (Table X).

EMG

During rest the EMG-amplitude was significantly increased in thetrapezius muscle of patients compared to controls (M-W.

Trap p=0.04). A similar but not quite significant increase was seen inthe temporal muscles (4-W.Temp p=0.10)(Table XI). Frequency valuesduring rest as well as all EMG values during MVC were not different fromthose of controls (Table XI).

Effect of Clenching on the Measured Tests

Tenderness

The median initial TTS was 12 (range 0-28) in patients who developedheadache and was increased significantly to 14 (range 0-33) at therecording 90 minutes after clenching (Wilc.p<0.001) (FIG. 10). Themedian TTS in patients who remained headache free was also 12 (range0-24) and remained 12 (range 0-33) after clenching (Wilc.p=0-33). Amarked, but not quite significant increase in TTS from 6 to 10 was seenin the few control subjects who developed headache (Wilc.p=0.06),whereas TTS only increased from 4 to 5 in controls who remained headachefree (Wilc.p=0.005)(FIG. 10).

Pressure Pain Thresholds

Pressure Pain Detection Thresholds in fingers and in the temporallegions remained constant in those subjects (patients as well ascontrols) who developed headache, whereas a significant increase of paindetection thresholds was seen in subjects who did not develop headache(Wilc. Patients fingers p=0.01;temp p=0.024; Controls fingersp=0.04;temp p=0.01)(FIG. 11A).

Pressure Pain Tolerance decreased in the parietal region in patients whodeveloped headache after clenching (Wilc.p=0.009), whereas thetolerances remained stable in patients who remained headache free.Pressure Pain Tolerances in the same region increased in controls whoremained headache free after stimulation (Wilc.p=0.003)(FIG. 11B).Pressure Pain Tolerance was stable in the hand and the temporal regionin all subjects without regard to headache development (FIG. 11B).

Thermal Thresholds

In patients as well as in controls, no significant differences inthermal thresholds were seen between those, who developed headache andthose who did not (FIG. 12).

EMG

During resting condition a significant decrease in amplitude value wasseen in the temporal and the trapezius muscles (for clenching both inpatients (Wilc.Temp.p<0.001, Trap.p<0.01) and in controls(Wilc.Temp.p<0.001, Trap.p<0.01). This decrease Was similar in those whodeveloped headache and in those who did not (FIG. 13A). In contrast,only the group of patients who developed headache showed decreasedamplitude values in the temporal muscle during MVC (Wilc.p=0.011) (FIG.13B)

Discussion

Studies in a general population and in specialized headache clinics haverevealed that increased muscle tenderness and frequent tooth clenchingare consistent findings in subjects with tension-type headache (Jensenet al. 1993b, Jensen et al. in prep., Wanmann et al. 1986, Langemark etal. 1987, Lous et al. 1982). Whether these relations are causal orsecondary to the pain has not yet been clarified. However, if there is acausal connection it should be possible to create an experimentalheadache model by interfering with these systems. Although severalattempts to make experimental pain in the chewing muscles have been made(Christensen et a. 1981, Clark et al. 1991, Bakke et al. 1989), only fewstudies have focused specifically on headache (Jensen et al. 1985,Magnusson et al. 1984). Jensen et al. reported that 54% of 48migraineurs developed a muscle-contraction like headache aftershortlasting sustained clenching (Jensen et al. 1985). These findingsindicate that headache subjects in general are more susceptible todevelop headache after sustained muscle contraction.

Relation Between Measurements in Patients and Controls Before Clenching

The finding of increased muscle tenderness b, manual palpation as themost significant difference between headache patients and healthycontrols supports previous findings in a general population (Jensen etal. 1993b). When selecting psycho-physiological measures it is importantto consider the information carried by the particular measure. Localtenderness as recorded by manual palpation is assumed to indicateincreased nociception from the free nerve endings in the connectivetissue of muscles, fascia and tendons (Jensen et al. 1990, Torebjork etal. 1984). Such increased nociception is probably due to a sensitizationor nociceptors by bradykinin, prostaglandines, substance P, 5-HT,histamine and potassiu (Mense et al. 1992, Jensen et al. 1992). Reducedmuscle blood flow leading to ischemia has been suggested as the cause oftenderness (Myers et al. 1983), but recently normal blood flow in thetemporal muscles of patients with chronic tension-type headache has beendemonstrated (Langemark et al. 1990).

Pressure Pain Thresholds

A decreased pressure pain detection threshold indicates a state ofallodynia, i.e. pain elicited by stimuli which normally are non-noxious.A decrease in pressure pain tolerance threshold indicates a state ofhyperalgesia, i.e. increased sensitivity for supra threshold noxiousstimuli, which may and may not coexist with allodynia (Jensen et al.1990). Identification of allodynia and hyperalgesia may therefore be ofspecial interest in the study of central and peripheral mechanisms ofnociception. In addition, we have studied responses from the hands andthe cranial regions in order to determine a possible anatomicalvariation in the response to pain stimulation. We also wanted to studythe muscular contribution and recorded thresholds from two neighboringcranial regions one with and one without interposed muscle. The factthat pressure pain detection thresholds and tolerances were lower in thetemporal region than in the nearby parietal region indicates thatmyofascial nociception contributes considerably to the recordedresponses. However, the finding of largely normal thresholds andtolerances in headache free patients indicates that the general painsensitivity in the cranial region is not permanently disturbed aspreviously suggested (Schoen

Thermal thresholds

Thermal rearm detection represents the activity in unmyclinated C-fibers(Campbell et al. 1989) whereas the heat pain detection representsactivation of cutaneous C-fibers responsive to mechanical and heatstimuli and their central modulation (Campbell et al. 1989). Inaddition, the myclinated A mechano heat fibers the may be activated whenthe heat pain tolerance is tested. If central pain perception isincreased, decreased warmth and heat pain thresholds are expected.However, thermal pain detection and tolerances were normal in theheadache patients suggesting normal pain sensitivity as discussed above.The present findings differ from a precious finding of decreased heatpain detection thresholds in patients with chronic tension-type headache(Langemark et al. 1989). In the prior study patients were, however, moreseverely affected and most of them had daily headaches and long lastingdrug overuse (Langemark et al. 1989). It is likely that chronic pain mayinduce central sensitization to incoming nociceptive signals, and thepreviously described decrease in noxious thresholds in severely affectedheadache patients may, therefore, be an effect of chronic pain ratherthan its cause.

EMG

It has been a widely held view that tension-type headache is caused byinvoluntary contraction of cranial muscles. Tile slightly increasedamplitude values during rest indicate that the pericranial muscles areinsufficiently relaxed (Jensen et al. 1994). However, this increase inEMG level was unaffected by the presence or absence of headache, and istherefore not likely to be a primary cause of pain (Jensen et al. 1994).The decreased amplitude values during maximal voluntary contraction inpatients developing headache and not in controls indicate that in someother way a muscular factor may be involved (Jensen et al. 1994).

Effect of Clenching on Headache and the Measured Tests

The present results indicate that sustained muscle contraction caninduce headache although the recordings have not been repeated during asimilar placebo provocation. An important finding is the increasedtenderness in subjects who developed headache. Headache had notdeveloped in the majority of subjects at 90 minutes after provocation,when the increased tenderness was recorded. This suggests that clenchingcauses tenderness, that tenderness precedes headache and that tendernessmay be one of the causes of the subsequent headache. A similar increasein tenderness scores during spontaneous attacks of tension-type headachehas recently been shown (Jensen et al. in press). Muscle tendernessusually requires several hours to develop (Christensen et al. 1981). Afurther increase in tenderness would therefore probably have beendetected if we had continued to record tenderness several hours afterclenching. In the present study, the experimental headache occurred witha lag time of one to several hours. In addition, the pain was mildinitially and gradually, in the course of hours, reached its peak. Incontrast, the intensity of headache in control subjects did not increaseafter onset. The very low VAS-score in controls may represent discomfortrather than clinical relevant pain as reported by the patients. Thusindicates that the and nociceptive system may be deficient in headachepatients. The exact degree of clenching seems to be of minor importance.Approximately the same percentage of subjects developed headache with10% of maximal contraction in the present study and with 5% or 30% ofmaximal contraction in the previous migraine study (Jensen et al.

Mechanisms of Tension-type Headache Suggested By the Present Results

The pressure pain detection thresholds remained stable in patients whodeveloped headache but increased in subjects who did not developheadache. We also found decreased pain tolerances in patients whodeveloped headache, unchanged values in the remaining patients andincreased values in controls, suggesting that headache patients do notactivate their antinociceptive system or that it is less effective inthese patients (Le Bars et al. 1979). On the other hand, their centralantinociceptive suppression is not so permanently and severely affectedthat it is reflected in permanent hyperalgesia, since the noxiousthresholds and tolerances were normal outside of a headache episode. Inaddition, as the thermal thresholds remained unaffected of the headachestate, no evidence for a general hypersensitivity to pain was found. Thesimilar decreases in EMG-levels in both groups after clenching indicatethat the increased BAG-levels in patients free of headache may be asecondary characteristic. This is supported by similar findings in arecent study of patients during and outside of spontaneous tension-typeheadache attacks (Jensen et al. in press). Based on the presentfindings, results from previous studies (Jensen et al. 1993b, Jensen etal. 1994, Jensen et al. in press) and results from recent animal studies(Mense et al. 1993, Le Bars et al. 1919) on peripheral and central painmechanisms we suggest the following mechanism of tension-type headache:involuntary contraction of muscles, due to mechanical or psychologicalstress, causes activation and chemical sensitization of the myofascialmechano receptors and their afferent fibres. This increased peripheralinput may result in sensitization and functional reorganization ofsecond order sensory neurons in the dorsal horn (Hoheisel et al. 1994)as stimuli in the deep myofascial tissues are much more effecting inthis respect than stimuli in the cutaneous tissues (Wall et al. 1984, Yuet al. 1993). Normally, increased peripheral nociceptive input iscounteracted by increased activity in the antinociceptive system and noheadache arises. However, in some individuals and under certaincircumstances this homeostatic mechanism does not function. An abnormalsensitization arises and combined with an impaired centralantinociceptive mechanism, an episode of tension-type headache maydevelop. However, the relative importance of peripheral and centralsensitization and of the antinociceptive system remain furtherelucidation. In conclusion, the results obtained be the presentinventors suggest that muscular factors play an important role in theinitiation of a headache episode. However, the further development andtransition into the chronic pain state is probably due to a centralsensitization with or without impairment of the central antinociceptivesystem.

TABLE VIII Clinical characteristics of the subjects studied TH patientsControls Number (n) 58 30 Males 22 12 Females 36 18 Age(years) 45 42(21-63) (23-67) Years with TH 23 —  (1-45) Frequency of TH 17 — days/28days  (8-27) Frequency of migraine  7 — days/year  (2-12) (n = 28) Meanvalues with range in brackets are given. TH indicates tension-typeheadache

TABLE IX Pressure pain detection thresholds (PPDT) and tolerances (PPTO)in 58 headache patients free of headache and 30 healthy controls. Meanvalues of left and right side with SD in brackets are given in kPa. PPDTPPTO FINGER patients 353(137) 779(294) controls 358(168) 785(289)TEMPORAL REGION patients *220(76)  399(146) controls 203(103) 387(157)PARIETAL REGION patients 323(146) 600(190) controls 317(195) 571(201) *p< 0.05

TABLE X Thermal thresholds in 58 headache patients free of headache andin 30 healthy controls. Mean values of left and right side with SD inbrackets are given in ° C. Warm Pain Pain detection threshold toleranceHANDS patients 34.5(1.2) 42.3(3.0) 47.2(2.3) controls 34.4(1.2)42.4(2.7) 47.5(2.2) TEMPORAL REGION patients *34.2(1.7)  39.6(2.7)44.0(2.0) controls 33.8(0.8) 39.1(2.7) 43.9(2.9) *p < 0.05

TABLE XI EMG levels in 58 patients free of headache and in 30 healthycontrols during rest and maximal voluntary contraction (MVC). Meanvalues of left and right side with SD in brackets are given; RMSindicate root mean square values of amplitudes (uV) and Mean F indicatemean frequency (Hz). REST MVC RMS Mean F RMS Mean F TEMPORAL MUSCLESpatients 2.7(1.9) 78(22) 164(81)  164(32) controls 2.3(0.9) 74(17)181(101) 155(30) TRAPEZIUS MUSCLES patients *3.5(1.2)  39(9)  246(124) 88(16) controls 3.1(0.9) 40(9)  259(131)  88(16) *p < 0.05

EXAMPLE 4 A Nitric Oxide Synthase Inhibitor is Effective in ChronicTension-type Headache and is Counteracting Central Sensitization

Introduction

Nitric oxide (NO) is an almost ubiquitous molecule that probably playsan important role in the modulation and transmission of pain (Meller andGebhart 1993). NO is assumed to be of particular importance for thedevelopment of central sensitization, i.e. increased excitability ofneurons in the central nervous system (McMahon et al. 1993; Meller andGebhart 1993). In this way NO may contribute to the development ofchronic pain. The synthesis of NO is catalyzed by, the enzyme NOsynthase (NOS) (Moncada et al, 1991). Resent animal studies have shownthat NOS inhibitors reduce central sensitization in persistent painmodels (Haley et al. 1992;Hao and Xu 1996; Mao et al. 1997). Chronictension-type headache responds poorly to analgesics and new treatmentsare badly needed (Rasmussen et a, 1991). The aim of the present study,to evaluate whether intravenous infusion of the NOS inhibitor, L-N^(G)methyl arginine hydrochloride (L-NMMA), is effective in the treatment ofthis disorder.

Materials and Methods

Subjects

Sixteen patients with a diagnosis of chronic tension-type headacheaccording to the criteria of the International Headache Society(Headache Classification Committee 1988) were recruited from theoutpatient headache clinic at Glostrup Hospital. There were 12 women and4 men with a mean age (range) of 38.5 (23-52) years. Five patients withcoexisting infrequent migraine (±one day/month) were accepted. Allpatients completed a diagnostic headache diary during a 4-week run-inperiod (Russell et al. 1992). At screening, a full physical andneurological examination, including 12-lead ECG were carried out. Bloodsamples for routine haematological and biochemical testing, and urinesample for urine analysis were taken. The patients were not allowed totake analgesics 12 hours prior to the treatment. Exclusion criteriawere: daily medication (including prophylactic headache therapy but notoral contraceptives); pregnant or breast feeding women; abuse ofanalgesics (corresponding to >2 gm of aspirin/day) or alcohol; serioussomatic or psychiatric diseases including depression (HamiltonDepression Score 317 (Hamilton 1960)); ischemic heart disease, a supinediastolic blood pressure>90 mmHg or heart rate<50 beats per minute atstudy entry. All patients gave written informed consent to participatein the study, which was approved by the local ethics committee andconducted in accordance with the Declaration of Helsinki.

Procedures

Using a double-blind crossover design, the patients were randomized toreceive 6 mg/kg L-NMMA (Clinalfa, Switzerland) or placebo (isotoneglucose) on two days with a typical episode of tension-type headacheseparated by at least one week. Randomization (Med. Stat) and drugpreparation were performed by staff not involved in the study. Themedication was given over 15 minutes into an antecubital vein (BraunPerfusor). The following parameters were measured at baseline and 15,30, 60 and 120 minutes post administration: headache intensity on a100-mm Visual Analog Scale VAS) (0—no headache and 100—worst imaginableheadache) and on a Verbal Rating Scale (ES) from 0-10 (0—no headache,5—moderate headache; 10—worst imaginable headache). Blood pressure andpulse rate were measured 5 minutes prior to administration of treatmentand at, 10, 11, 20, 25, 30, 60, 90 and 120 minutes post administrationTwelve-lead ECG was monitored continuously. Any adverse events wererecorded. Patients with unrelieved headache at 120 minutes posttreatment were allowed to take rescue medication, All patients wereasked to record details of the following on a diary card at 4, 8, 12,16, 20 and 24 hours post administration. headache intensity on VRS, anymedication taken and adverse events. Between 4-7 days after eachtreatment, the patients returned to the clinic, the diary cards werecollected and any adverse events were noted.

Data Analysis and Statistics

Primary endpoint was the reduction of pain intensity over time on activetreatment compared to placebo. The secondary endpoints were reduction ofpain intensity at 30, 60, 90 and 120 minutes post dosing on VAS and VRScompared to pre-treatment pain score within each treatment. Comparisonof pain intensity on VAS, blood pressure and pulse rate over timebetween treatments were performed with ANOVA. Paired -Samples T Test wasused to compare pre-treatment pain score on VAS with pain score at 30,60, 90, 120 minutes post dosing within each treatment. The sum ofdifferences between the pre-treatment VRS score and the VRS score at 30,60, 90, 120 minutes post dosing was calculated in order to obtained asummary measure of pain score for each treatment (Matthews et al. 1990).These sums of differences for each treatment where compared by WilcoxonSigned Rank test. Five percent was accepted as level of significance.

Results

Treatment Efficacy

L-NMMA reduced pain intensity (VAS) over time significantly more thanplacebo (p=0.007). Relative percent changes in pain intensity frombaseline are shoe in FIG. 14. Pain score was significantly reduced after30, 60, 90 and 120 minutes post treatment with L-NMMA (Table XII), Therewas no significant reduction in pain intensity following treatment withplacebo at any time points. The pain intensity on VRS was significantlylower after treatment with L-NMMA than after treatment with placebo(p=0.02).

Adverse Events and Rescue Medication

The mean arterial blood pressure (MAP) and pulse rate changedsignificantly over time during treatment with L-NMMA compared withplacebo (p=0.0001 and p=0.0001). The maximum increase in MAP was 12=12%and occurred 15 minutes post dosing. The maximum decrease in pulse ratewas 16±2% and occurred 10 minutes post dosing. The increase in MAP anddecrease in pulse rate are consistent with known pharmacologicalproperties of L-NMMA. Patients were unaffected by these changes. Sevenpatients reported subjective symptoms in relation to the L-NMMA infusionThese were: tiredness (2), dryness of the mouth (3), drowsiness (1),exhaustion (1)! nausea (1) and a feeling of tingling in arm (1). Fourpatients reported subjective symptoms in relation to placebo treatment.These were: a feeling of tingling in arm (2) and shoulder (2), drynessof the mouth (1), warm sensation in the body (1) and drowsiness (1). Nopatients withdrew from the study because of side effects, Three patientstreated with L-NMMA and 7 patients treated with placebo used simpleanalgesics as rescue medication.

Discussion

There is ample experimental evidence showing that persistent activity inperipheral nociceptors may lead to sensitization of spinal dorsal hornneurons partly via activation of N-methyl-D-aspartate (NMDA) receptors(Coderre et at, 1993). Since many of the effects of the NMDA receptoractivation are mediated through production of NO, it seems probable thatNO plays an important role in the hyperalgesia in the spinal cord(Metier and Gebhart 1993). In support for this, animal models have shownthat NOS inhibitors reduce spinal dorsal horn sesitization induced bycontinuous painful input from the periphery (Haley et al. 1992; Hao andXu 1996; Roebe et al. 1996). However, the efficacy NOS inhibitors havenot previously been examined in patients.

Recently, it has been demonstrated that spinal dorsal horn sensitizationdue to prolonged nociceptive input from pericranial myofascial tissuesprobably plays an important role in the pathophysiology of chronictension-type headache (Bendtsen et al. 1996a, 1996b, Jensen et al.1997). Thus, it is likely that the analgesic effect of L-NMMA in chronictension-type headache is due to reduction of central sensitization atthe level of the spinal dorsal horn.

In conclusion, the present study provides the first evidence of aneffect of NOS inhibitors in human chronic pain, and indicates that theeffect of NO is via reduction of central sensitization probably at thelevel of the dorsal horn/trigeminal nucleus.

TABLE XII Pain scores on VAS before treatment and at 30, 60, 90 and 120minutes post dosing. Mean values (SD) are given. 30 60 90 120 Baselineminutes minutes minutes minutes L-NMMA 49 ± 16 33 ± 18*  35 ± 18*  34 ±21*  33 ± 21*  Placebo 44 ± 14  41 ± 17^(NS)  40 ± 17^(NS)  42 ± 16^(NS) 40 ± 17^(NS) * = p < 0.05 and NS = not significant compared withpretreatment values (Paired-Samples T Test).

EXAMPLE 5 Muscular Factores Are of Importance in Tension-type Headache

Introduction

A recent study from by the present inventors demonstrated for the firsttime that chronic tension/type headache has a physiological basis and iscaused at least partly by qualitative changes in the central processingof sensory information (Bendtsen et al. 1996b). It was suggested thatmuscular disorders are of primary importance for the development ofcentral sensitization To test this hypothesis, the present study of thepsychophysical tests suggested in the IHS classification (headacheClassification 1988) as well as thermal pain sensitivity was conducted.The primary aim was to compare the mechanical and the thermal painsensitivity in tension-type headache patients with and without disordersof pericranial muscles. The secondary aim was to study the clinicalcharacteristics of these patients.

Patients and Methods

Patients

Fifty-eight patients with tension-type headache fulfilling theIHS-criteria (Headache Classification 1988) were included (Table XIII).Twenty-nine patients had frequent episodic tension-type headache (ETH)and 29 patients had chronic tension-type headache (CTH). The patientswere recruited from the out-patient headache clinic at Gentofte Hospitaland complete physical and neurological examinations were done beforeentry. According to the primary aim patients with restricted tendernessin the pericranial muscles were favoured, since the percentage ofpatients associated with muscular disorders is 80-90% in consecutivepopulations (Jensen et al., 1996, Langemark et al., 1988). Furtherinclusion criteria were duration of tension-type headache for at leastone year and age between 18 and 70 years. The exclusion criteria were:migraine more than 1 day per month, cluster headache, trigeminalneuralgia, other neurological, systemic or psychiatric disorders,ingestion of major medications including prophylactics for migraine orother headaches, any form of drug abuse or dependence as dailyergotamine or large amounts of plain analgesics.

Thirty healthy subjects (12 males and 18 females) with a mean age of 42years (range 23-67 years) and without tension-type headache (<14 daystension-type headache/year) were used as controls. Informed consent wasobtained and the study was approved by the local ethical committee. Thepresent study was a part of a multifaceted study of tension-typeheadache, of which other parts have been published previously (Jensen,1996, Jensen and Olesen, 1996).

Procedure

All patients had to fill in a diagnostic headache diary during a 4 weekran-in period to ensure that they fulfilled the inclusion criteria.Patients were instructed to fulfill the diary at the end of each daywith headache and to record the mean intensity on a 0-3 scale, where 0was no pain and 3 was severe incapacitating pain thy requires bed rest(Russel et al., 1992). The approximate start and disappearance ofheadache and the total intake of analgesics or other medications shouldalso be recorded. A standard dose of analgesics was defined as a doseequivalent to 1000 mr of aspirin. All patients were examined when freeof headache and were not allowed to have taken any analgesics on the dayof examination.

Examination

The examination was performed in a standardized way, which has beendescribed previously (Jensen, 1996, Jensen and Olesen, 1996). Alrecordings were performed by the same observer, the technician,throughout the entire study and the observer was blinded for thefollowing subdivision of patients. Before recordings of pain thresholdseach individual was carefully instructed to apply the sameinterpretation of ‘painful’ throughout the study. Initial test sessionswere applied to all subjects in order to familiarize them with the testconditions.

Palpation

Pericranial tenderness as evaluated by palpation of 9 pairs ofpericranial muscles and tendon insertions by the technician in astandardized, randomized procedure (Langemark and Olesen, 1989, Jensenet al., 1993b, Bendtsen et al., 1995a). Tenderness was scored in eachlocation according to an ordinal scale from 0 to 3, and scores from allsites were summated. The maximum possible score was thus 54 points. ThisTotal Tenderness Score system(CTS) (Langemark, and Olesen, 1987) haspreviously proved to be reliable (Bendtsen et al., 1995). We havepreviously demonstrated that the most ideal Cut-off point for separatingtension-type headache subjects from non-headache subjects with respectto muscle tenderness was the 75% quartile of TTS obtained from a generalpopulation, whereas pressure algometry and EMG provided no fartherinformation (Jensen et al., 1996). In the following, ITS is used as theonly criteria for further subdivision patients with TITS above 9 (equalto the 75% quartile of TTS from healthy controls) was classified ashaving an association with muscular disorder (MUS), whereas those withTTS value at 9 or below were classified as unassociated with such adisorder (non-MUS).

Pressure Pain Thresholds

The pressure pain thresholds were evaluated bilaterally on the distaldorsal part of the second finger, and in two cranial locations, one withinterposed temporal muscle (Temp) and one without interposed muscle inthe parietal region (Par). A standardized and previously evaluatedmethod ads applied using an electronic pressure algometer (Somedic AB,Sweden) with an 0.79 cm² circular stimulation probe (Petersen et al.,1992, Jensen et al., 1986, Brennum et al., 1989). Two pain qualitieswere recorded, the Pressure Pain Detection Threshold (PPDT) defined asthe threshold, where the pressure sensation became painful, and thePressure Pain Tolerance (PPTO) defined as the threshold where thepatient would no longer tolerate the pain (Petersen et al., 1992). Bypressing a hand held button the subjects indicated that the thresholdwas reached, and the pressure was released immediately. If patients didnot activate the button, the experiment was terminated when reaching 800kPa in the cranial region and 1500 kPa in the fingers. Each thresholdwas calculated as the median value of 3 determinations performed withintervals of 10-15 seconds, and mean values of left and right sidedrecordings are presented in the following.

Thermal Pain Thresholds

Thermal thresholds were evaluated with a computerized version of theThermotest (Somedic AB, Sweden) (Fruhstorfer et al., 1976, Yanmitsky etal., 1995). The thermode consisted of series-coupled Peltier elementsand measured 25×30 mm. The thenar region of the hand and the anteriorpart of the temporal region were examined bilaterally. Three stimulationqualities were recorded; the Warm Detection limit (WD) defined as thelowest temperature detected as warm, the Heat Pain Detection HPD)defined as the temperature where the heat sensation became painful, avidthe Heat Pain Tolerance (HPTO) defined as the highest temperaturetolerated (Jensen et al., 1996, Jensen and Olesen, 1996). A baselinetemperature of 32 ac and a 1.0° C./sec rate of temperature change wasused. Heat stimulation was terminated when reaching 52° C., if thepatients had not responded before. By pressing a hand-held button thesubjects indicated when the actual threshold was reached. This value wasrecorded automatically and the stimulator returned to baseline. Eachthreshold was calculated as the average of 5 determinations performedwith intervals of 10-15 seconds, and mean values of left and right sidedrecordings are presented in the following.

Electromyography

EMG signals from the temporal and trapezius muscles were recordedbilaterally by a 4-channels electromyograph (Couiterpoint, Dantec,Copenhagen). A standardized, previously described method was applied(Jensen et al., 1993). Data were collected during rest in the supineposition and during maximal voluntary contractions (MVC) (Jensen et al.,1996), The root mean square (RMS) voltage was measured Power spectrumvas calculated for the frequency range 0 to 1 kHz and Mean Frequencies(Mean F) were extracted (Jensen et al., 1996).

Statistics

Clinical data are presented as mean values with range C(able XII and NV)and the psychophysical data as mean values±SE. Mann-Whitney's U test wasused for testing unpaired observations in patients with and withoutassociation with muscular disorders. Analysis of variance was used tocontrol for the variations in sex distribution among the groups.Spearman's test was used for calculation of coefficients of correlation.Five percent was accepted as level of significance.

Results

Two patients (a male with the episodic and a male with the chronicsubform) were excluded from the present study due to deficient diaries.The remaining 56 patients, 28 with CTH and 28 with ETH completed thestudy and detailed clinical data with respect to their association withmuscular disorder are presented in Table XIII and Table XIV. Fourteenpatients with chronic tension-type headache had a history of coexistingmigraine with a mean value of 7.3 days with migraine per yea, notsignificantly different from the 15 ETH patients, who had a history of7.7 days with migraine per year. Similarly, there was no significantdifference between the prevalence of migraine in patients with musculardisorders compared to those without such disorder. No significantvariations in the clinical characteristics between patients with andwithout disorders of pericranial muscles could be detected (TableXIII,XIV).

Tenderness Recorded By Manual Palpation.

According to the prior definition of association with musculardisorders, CTH patients associated with muscular disorder (MUS) had, asexpected, significantly higher ITS at 18.5 compared to 6.2 in thosewithout such an association (non-MUS) (p<0.0001). Similarity, ETHpatients with MUS had significantly higher ITS at 15.3 compared to 4.3in those without such an association (p<0.0001).

Pressure Pain thresholds

Pressure pain detection and tolerance thresholds were significantlylower in CTH patients associated with MUS compared to non-MUS patientsin all the examined locations (PPDT p<0.001; PPTO p<0.05) (Table XV)(FIG. 15).

In patients with ETH, there wore no significant differences in thepressure pain thresholds and tolerances between subjects with or withoutassociation with muscular disorders in any of the examined locations(Table XVI) FIG. 16).

Thermal Pain Thresholds

There were no significant differences in heat detection, heat pain andheat pain tolerance thresholds from the hands and the temporal regionsbetween CTH patients with and without a muscular disorder. Similarly, nosignificant variations in thermal thresholds could be detected in ETHpatients with and without a muscular disorder.

Relation Between Tenderness and Pain Thresholds

In CTH patients, the Total Tenderness Score (TTS) was lightly correlatedto the mechanical pain thresholds at the temporal region (Temp. TTS vsPPDT:r=−0.61, p<0.001; TTS vs PPTO:r=−0.65, p<0.001), and a similartendency was seen at the parietal region (TTS vs PPDT r=−0.59, p=0.003;TTS vs PPTO r=−0.24, p=0.27) and at the extracephalic region (Hands: ITSvs PPDT r=−0.36, p=0.06, TTS vs PPTO, r=−0.48, p=0.02). No suchrelations could be detected in ETH patients in any of the examinedlocations. When TTS was correlated to thermal thresholds no significantrelations appeared either in the chronic or the episodic form.

EMG

When EMG levels were recorded from the temporal and the trapeziusmuscles under resting conditions and during maximal voluntarycontraction, CTH patients with association to muscular factors hadsignificantly higher RMS values in their trapezius muscles duringresting condition compared to non-MUS patients (p=0.02). No othersignificant differences between the 2 subgroups in neither CTH nor ETHpatients appeared.

Relation to Healthy Controls

Tenderness By Manual Palpation

The mean Total Tenderness Score(TTS) in the 30 healthy controls was 4.7(quartiles 0-9) and was significantly lower than 9.8 (quartiles 4-15) inthose 28 patients with ETH p=0.002). In CTH patients TTS was 14.1(quatiles 4-15) and significantly higher than in ETH patients (p=0.03)and in healthy controls (p<0.0001).

Pressure Pain Thresholds

Compared to healthy controls, CTH patients with non-MUS hadsignificantly higher pressure pain thresholds and tolerance thresholdsin all the examined locations (p<0.01), whereas the mechanicaltolerances tended to be significant lower in CTH patients with MLJS(Fingers PPTO, p=0,07; Temp PPTO p=0.05). No significant differencescould be detected in the parietal regions or in pressure pain detectionthresholds from the other locations. When pressure pain detection andtolerance thresholds from the 2 subgroups of ETH patients were comparedto those from healthy controls no significant differences appeared.

Thermal Pain Thresholds

When the thermal thresholds were compared to healthy controls,significantly higher values of all the tested qualities were noted incephalic locations in those 10 CTH patients without association withmuscular disorders, whereas only warm detection values were higher onthe hands of these patients (Temporal:WD p=0.02,WPDT p=0.04,WPTOp=0.028;Hands:WD p=0.02). No significant variations in thermalthresholds could otherwise be detected in relation to healthy controls.

EMG

Only CTH patients associated with muscular factors had significantlyhigher RMS values in the temporal (0.008) and the trapezius musclesduring rest (p=0.004) than healthy controls. No other differencesbetween patients and controls were noted.

Discussion

Relation Between Tenderness and Pain Thresholds

In the present study highly significant inverse correlations betweenTTS, pressure pain detection and tolerance thresholds were found inpatients Faith CTH corresponding with our recent study (Bendtsen et al.1996). Others have reported relatively small and clinicallyinsignificant relations (Schoenen et al. 1991a, Jensen et al., 1996,Sandrini et al., 1994), and the pressure pain thresholds provided onlylimited diagnostic value (Jensen et al., 1996). This discrepancy may bedue to the fact that the pressure pain threshold represents the lowerend, and the pressure pain tolerance the upper end of a pain stimulusresponse curve. Tenderness obtained by manual palpation elicit painintensities between these extremes where the difference between patientsand controls is largest as discussed recently by Bendtsen et al(Bendtsen et al., 1996b, Bendtsen et al., 1996c). The diagnostic testsgiven in the IHS classification were previously assessed in a study froma highly specialized headache clinic (Snadrini et al., 1994) and insubjects from a general population (Jensen et al., 1996). In the latterstudy, 87% of subjects with chronic, and 66% of subjects with episodictension-type headache had a disorder of die pericranial muscles (Jensenet al., 1996). In the former, Sandrini et al reported that 61% ofpatients with episodic, and 66% of patients with chronic tension-typeheadache had disorder of pericranial muscles. An earlier stud, whereonly EMG and pressure algometry were assessed, 72% were found to beassociated with disorders of pericranial muscles (Schoenen et al.,1991). Tenderness determined by manual palpation was previously found tobe the most sensitive and specific test for disorder of pericranialmuscles (Jensen et al., 1996) and was therefore applied as the only testto separate the 2 subforms in the present study.

Pathophysiological Mechanisms of the Disorders of Pericranial Muscles

It has been uncertain whether the increased, pericranial myofascialtenderness was the cause or the effect of the pain. A recentexperimental study indicated, however, that tenderness precedes theinduced headache by several hours when tension-type headache is inducedby tooth clenching (Jensen et al., 1996). Possible mechanisms for thetenderness include 1) sensitization of peripheral myofascialnociceptors; 2) sensitization of second order neurons at thespinal/trigeminal level; 3) impaired central modulation of thenociceptive activity.

As tension-type headache is a disease in man and not known in animals,experimental animal models are of limited value for evaluation of thesemechanisms. Fortunately, quantitative analyses of mechanical and thermalpain thresholds in humans can be used for this purpose. Thermal pain-and tolerance thresholds are normal in most of these patients, whichindicates that pain mediated by C-fibers is registered and modulatednormally. The present finding of markedly increased tenderness, slightlydecreased mechanical but normal thermal thresholds at cephalic andextracephalic locations in CTH patients associated with musculardisorder, strongly indicates a hyperalgesic response to mechanicalstimulation in these patients in line with previous studies (Bendtsen etal., 1196c, Schoenen et al., 1991b, Langemark et al., 1989). This isalso supported by our findings of a highly significant inverse relationbetween tenderness and mechanical threshold. It has recently beendemonstrated that due to central sensitization, pain in CTH and infibromyalgia may be mediated via low-threshold mechanosensitiveafferents projecting to dorsal horn neurons (Bendtsen et al., 1996c,Bendtsen et al. in press). This is supported by prior observations byBendtsen et al., where an abnormal qualitative stimulus responsefunction was found only in those 20 CTH patients with the mostpronounced tenderness whereas 20 patients without abnormal tendernessexhibited a fairly normal stimulus response curve (Bendtsen et al.1996c). A Anther support for myofascial involvement is the finding ofincreased EMG amplitude levels only from the pericranial muscles of CTHpatients associated with muscular disorders, whereas EMG levelsotherwise were similar to those in controls. The mechanisms of pain intension-type headache without 6% association with a muscular disordercannot be explained by simple allodynia and/or hyperalgesia as bothmechanical and thermal pain thresholds from these patients weresignificantly increased compared to healthy controls, indicating ahigher pain tolerability. Therefore, other mechanisms, probably in thecentral modulation of pain, must be considered. As the clinical featuresexamined in the present study were fairly similar between the 2subgroups in both the episodic and the chronic form it is very likely,however, that several pathophysiological mechanisms are shared and weredocumentation about the fairly rare patients with tension-type headachewithout association with muscular disorders are highly needed. Takentogether our data strongly suggest that central sensitization is of keyimportance in chronic tension-type headache with disorders ofpericranial muscles, whereas other mechanisms must be considered inpatients without such disorders.

Relationship Between Episodic and Chronic Tension-type Headache

The present study is the first study which have examined this widevariety of clinical characteristics and psychophysical tests in bothepisodic and chronic tension-type headache. A marked difference innociceptive mechanical thresholds between the 2 subgroups in thechronic, but not in the episodic form was demonstrated, whereastenderness recorded by manual palpation was highly increased in both theepisodic and the chronic tension-type headache. A hypothesis of thepathophysiological evolution of tension-type headache can therefore becreated. In ETH patients with disorder of pericranial muscles, the mostlikely mechanism is a slightly increased input from myofascialnociceptors projecting to a widely normal central pain perceptionsystem. As chronic tension-type usually evolves from the episodic form(Langemark et al., 1989) it is suggested that prolonged painful inputfrom the periphery may sensitize the central nervous system and that thepain in CTH associated with muscular disorder thus may be due to acentral misinterpretation of the incoming signals at the dorsal horn ortrigeminal level. Such mechanisms have been demonstrated in animalmodels (Coderre et al., 1993, Mense et al., 1993, Hu et al.,1992,Hoheisel et al. 1994), and irritative stimuli from myofascial, deeptissues are found to be much more effective for induction of centralsensitization than cutaneous stimuli Mu et al., 1993). Musculardisorders may therefore be of major importance for the conversion ofepisodic into chronic tension-type headache. As die most frequentlyreported precipitating factors leading to tension-type headache arestress, mental tension and tiredness (Rasmussen et al., 1993, Clark etal., 1995, Ulrich et al., 1996), central supraspinal involvement isundoubtedly also involved although precipitating factors may bedifferent from causative factors, Whether the precipitating factors andthe evolution of pain vary between the patients with and with disordersof pericranial muscles remains to be elucidated.

In conclusion, the present data indicate that the fine balance betweenperipheral nociceptive input and their central modulation seems to bedisturbed in the majority of patients with tension-type headache, namelythose associated with muscular disorders. An a central misinterpretationof the incoming peripheral stimuli may be the result, a vicious circleis started and is probably maintained long time after the primaryeliciting stimuli/stressor had stopped. Disorders of pericranial musclesmay therefore be of major importance for the conversion of episodic intochronic tension-type headache, whereas other mechanisms should beconsidered for those patients without such disorders. The present studysupplements the understanding of the interaction between peripheral andcentral changes in tension-type headache, and thereby, hopefully, willlead to a better understanding, prevention and treatment of the mostprevalent type of headache.

TABLE XIII Clinical characteristics of patients with chronictension-type headache (N = 28) Patients Patients with MUS without MUSNumber (n) 18 10 Males/females 7/11 7/3 Age (years) 48.1 49.4 (34-64)(37-59) Years with TH 24.8 26.2  (1-45)  (2-50) Frequency of TH 22.623.7 (days/28 days) (15-28) (15-28) Intensity  1.7  1.4 (0-3 scale)  (1-2.5) (1-2) Duration 11.3  9.5 (hours) (4.2-24)  (2.9-24) Medication  1.6  1.8 (doses/day)   (0-3.1)   (0-4.1) Mean values withrange in brackets are given. MUS indicate association with musculardisorder as defined in the text, and without MUS indicate no suchassociation. TH indicates tension-type headache.

TABLE XIV Clinical characteristics of patients with episodictension-type headache (N = 28) Patients Patients with MUS without MUSNumber (n) 14 14 Males/females 1/13 5/9 Age (years) 39.8 42.6 (20-56)(21-59) Years with TH 20.2 19.6  (2-40)  (8-30) Frequency  9.6 10.0(days/28 days)  (5-14)  (6-14) Intensity  1.7  1.8 (0-3 scale) (1.0-2.1)(1.4-2.2) Duration  9.7  8.6 (hours) (4.7-18)  (3.3-24)  Medication  1.0 0.8 (doses/day) (0-2)   (0-1.4) Mean values with range in brackets aregiven. MUS indicate association with muscular disorder as defined in thetext, and without MUS indicate no such association. TH indicatestension-type headache.

TABLE XV Pressure pain detection and tolerance thresholds in patientswith chronic tension-type headache (N = 28). Mean values are given inkPa with SE in brackets. Patients Patients with MUS without MUS (n = 18)(n = 10) p-value Pain detection thresholds Fingers 262(17) 374(23) p <0.001 Temporal region 143(9)  241(18) p < 0.0001 Parietal region 217(18)368(28) p < 0.001 Pain tolerance thresholds Fingers 535(32) 776(50) p <0.001 Temporal region 252(17) 394(23) p < 0.0001 Parietal region 471(38)521(27) p = 0.04

TABLE XVI Pressure pain detection and tolerance thresholds in patientswith episodic tension-type headache (N = 28). Mean values are given inkPa with SE in brackets. Patients Patients with MUS without MUS (n = 14)(n = 14) p-value Pain detection thresholds Fingers 247(12) 269(18) p =0.14 Temporal region 162(10) 169(10) p = 0.72 Parietal region 223(16)221(16) p = 0.89 Pain tolerance thresholds Fingers 610(34) 595(50) p =0.47 Temporal region 317(18) 327(23) p = 0.98 Parietal region 453(23)449(30) p = 0.85

EXAMPLE 6 Gabapentin Has a Prophylactic Effect in Chronic Tension-TypeHeadache

Introduction

GABA is an important inhibitory transmitter in the central nervoussystem and it has been suggested that the encoding of low-thresholdmechanical threshold stimuli depends upon the presence of a tonicactivation of intrinsic glycine and/or GABAergic neurons (Yash andMalmberg 1994). Gabapentin was synthesized to be a systemical activeGABA analogue and was found to have anticonvulsant effect. Althoughinitially employed in humans to control seizures, recent clinical casesindicated that the agent showed efficacy in treating human neuropathicpain states (Rosner et al. 1996), and a considerably effect in severalexperimental pain models (Hwang and Yaksh 1996, Xiao and Bennett 1996).The exact mechanism is not full understood, but several mechanisms havebeen suggested. Binding studies fail to show affinity for either GABA Aor GABA B, although Gabapentin can increase the rate of GABA synthesisand release. Furthermore, Gabapentin showed binding affinity to thealpha-2-subunit of a calcium channel (Gee et al. 1996), and thesecalcium channels are recently reported to play a very exciting role inthe genetic studies of migraine disorders. As the side effect profile ofGabapentin is favorable, the prophylactic effect of Gabapentin in asmall open labeled pilot study in patients with chronic tension-typeheadache was evaluated.

Materials and Methods

Three patients with a diagnosis of chronic tension-type headacheaccording to the International Headache Society (Headache ClassificationCommittee 1988) were recruited from the outpatient headache clinic atGlostrup Hospital. The patients were males with a mean age of 42 years(range 35-49). The mean life time duration of chronic tension-typeheadache was 16 years (range 7-2 1). Two patients had a coexisting butinfrequent migraine. Exclusion criteria were; daily major medication(including prophylactic headache therapy); abuse of analgesics oralcohol; serious somatic or psychiatric diseases including depression.

Procedures

Using an open labeled design, patients fulfilled a diagnostic headachediary during at least 4 weeks run-in period to ensure the diagnosticcriteria Thereafter, the patients received Gabapentin (Neurontin®)tablets, initially 300 mg (one tablet) per day on day one, increasingwith 300 mg (1 tablet) per day to 900 mg (3 tablets) on day 3. Thetreatment period lasted 4 weeks, and during this period patients wereasked to continue with headache diaries, and record headache intensity,frequency, duration, any medication taken and any possible adverseevents. At a follow, up visit at day 29-32, diaries were collected andany adverse events and evaluation of the treatment were recorded. Due tothe low number of patients, no statistical analysis were done. Theprimary efficacy parameters were headache intensity, frequency andduration, and the mean values from the run-in period were compared tothose obtained during the treatment period.

Results

All patients completed the study. Headache intensity decreased 35%,namely from 5.5 on a 0-10 VAS intensity scale during run-in period to3.6 during active treatment. Duration of the individual headache episodewas reduced by 8%, and frequency, of headache decreased by 45%, namelyfrom 23.5 days per 4 weeks during run-in period to 13 days per 4 weeksduring the active treatment period. The mean daily intake of analgesicsdecreased by 72% from 1.1 dose per day to 0.3 dose per day. One patienthad excellent effect of Gabapentin with complete relief of the headacheafter 2 days treatment, another patient had a moderate effect onheadache intensity and frequency, and the third patient had nosignificant effect on any of efficacy parameters. Those two subjectswith good or excellent effect reported no side effects, whereas thethird patient who had no beneficial effect of Gabapentin complained ofsedation, vertigo and slight nausea. These side effects disappearedcompletely after cessation of the drug intake.

Discussion and Conclusion

The present results suggest a positive prophylactic effect of Gabapentinin chronic tension-type headache, which is in accordance with thepredictions made from the model involving central sensitization providedby the present invention. Although the exact mechanism of action ofgabapentin is not fully elucidated, the preliminary experimentalevidence are highly in favor of a pathophysiological explanation ofchronic tension-type headache, as caused by central sensitization,

EXAMPLE 7 Dextromethorphan Has a Prophylactic Effect in ChronicTension-type Headache

Introduction

The common role played by NOVA antagonism in preclinical models isconsistent with the observation that systemic ketainine reduces thealiodynia, hyperalgesia and after sensation present in patients withperipheral pain injury, and the magnitude of the relief is, in general,proportional to dose. Detromethorphan has been shown to reduce the aftersensation induced by repetitive stimuli in human volunteers (Price et al1994). Furthermore, the NMDA receptors are shown to act on the neuronalexcitability via opening or closing of ion channels. The increase inintracellular calcium by such opening of the ion channels is believed toinitiate a cascade of biochemical events, including pain. Effectiveblockade of these events is possible by NMDA antagonists, which are alsohighly effective in various human pain conditions related to centralsensitization (Person et al 1995). The major problem in this treatmentstrategy is, however, the central side effects of most NMDA antagonists.Dextromethorphan has been known for decades as a cough suppressant andhas a very favorable side effect profile. Therefore the prophylacticeffect of Dextromethorphan was evaluated in a small, open labeled pilotstudy in patients with chronic tension-type headache.

Materials and Methods

Five patients with a diagnosis of chronic tension-type headacheaccording to the International Headache Society (Headache ClassificationCommittee 1988) were recruited front he outpatient headache clinic atGlostrup Hospital. There were 2 males and 3 females, and the mean agewas 45.4 years (range 39-48). The mean life time duration of chronictension-type headache was 12.2 years (range 4-25). One patient badcoexisting but infrequent migraine. Exclusion criteria were: daily majormedication (including prophylactic headache therapy); abuse ofanalgesics or alcohol; serious somatic or psychiatric diseases includingdepression.

Procedures

Using an open labeled design, patients fulfilled a diagnostic headachediary during at least 4 weeks run-in period to ensure the diagnosticcriteria. Thereafter, the patients received Dextromethorphan (Dexofan®)tablets at 30 mg each, three times per day. The treatment period lasted4 weeks, and during this period patients were asked to continue withheadache diaries, and record headache intensity, frequency, duration,any medication taken and any possible adverse events, At a follow upvisit at day 29-32, diaries were collected and possible adverse eventsand evaluation of the treatment were recorded. Due to the restrictednumber of patients, no statistical analysis were done. The efficacyparameters were headache intensity, frequency and duration, and intakeof simple analgesics. Mean values from the run-in period were comparedto those obtained during the treatment period.

Results

All patients completed the study. The intensity of headache was reduced18% namely from 4.4 on a 0-10 VAS intensity scale during the run-inperiod to 3.6 during active treatment. Duration of the individualheadache episode was reduced by 11%, and frequency of headache decreasedby 4%, namely from 28 days per 4 weeks period during run-in to 27 daysper 4 wrecks period during active treatment. Intake of analgesicsdecreased by 79% from a mean intake at 1.8 dose per day during ran-inperiod to 0.5 dose per day during active treatment. Two patientsreported a marked eject with considerable relief of headache intensityand duration within very few days of treatment, one patient had a slightrelief of headache intensity and two patients reported no effect at all.Four patients reported no side effects, and marked side effects withsedation was reported in one patient, the patient with best clinicalresponse. These side effects diminished considerably after a dosereduction to 40 mg per day.

Discussion and Conclusion

The present results suggest a positive prophylactic effect ofDextromethorphan in chronic tension-type headache. The lack of effect insome patients may be due to a relatively small dosage. Although theexact mechanism of Dextromethorphan is not fully elucidated, thepreliminary evidence in experimental pain model is in favor of an effectaccording to the present, pathophysiological model of chronictension-type headache, i.e. the central sensitization model of thepresent invention.

EXAMPLE 8 Possible Mechanisms of Action of Nitric Oxide SynthaseInhibitors in Chronic Myofascial Pain

Pain from the musculoskeletal system is probably the most common type ofchronic pain (Magni et al. 1990). Progress in basic pain research hasincreased our knowledge about the mechanisms underlying chronicmyofascial pain (Mense 1993). Thus, substantial experimental evidenceindicates that central sensitization generated by prolonged nociceptiveinput from the periphery plays an important role in the pathophysiologyof chronic pain particularly from myofascial tissues (Woolf 1983;Hu etal. 1992; Woolf and Doubell 1994; Bendtsen et al. 1996a). The freelydiffusible gas nitric oxide (NO) is assumed to be of importance for thedevelopment of central sensitization (McMahon et al. 1993; Meller andGebhart 1993). Thus, nitric oxide synthase (NOS) inhibitors reducecentral sensitization in animal models of persistent pain (Haley et al.1992; Hao and Xu 1996; Mao et al. 1997). We recently demonstrated thatNOS inhibition has an analgesic effect in patients with chronicmyofascial pain (Ashina et al. 1998a), However, the mechanisms of thiseffect have so far been unknown. The aim of the present study was toinvestigate whether the NOS inhibitor, L-N^(G) methyl argininehydrochloride (L-NMMA), modulates muscle hardness (Sakai et al. 1995)and myofascial tenderness (Jensen et al. 1998) in patients with chronicmyofascial pain.

Materials and Methods

Subjects

Sixteen patients with a diagnosis of chronic tension-type headacheaccording to the criteria of the International Headache Society(Headache Classification Committee 1988) were included (Table XVII).Five of the patients had cocking infrequent migraine (<four days/year).The patients were recruited from the out-patient headache clinic atGlostrup University Hospital without respect to presence or absence ofmyofascial tenderness. All patients underwent a general physical and aneurological examination and completed a diagnostic headache diaryduring a 4-week run-in period (Russell et al. 1992). Exclusion criteriawere; daily medication (including prophylactic headache therapy but notoral contraceptives); abuse of analgesics (corresponding to >2 gm ofaspirin/day); serious somatic or psychiatric diseases includingdepression (Hamilton Depression Score #17 (Hamilton 1960)). Patientswere examined and treated during a typical day of tension-type headache.All patients gave written consent to participate in the study, which wasapproved by die Danish Board of Health and the local ethics committee.The study was conducted in accordance with the Declaration of Helsinki.

Apparatus

Muscle Hardness.

The muscle hardness of the trapezius muscle was measured with a hardnessmeter, which has previously been described in detail (Horikawa et al.1993). In brief, the hardness meter consists of a laser distance sensorand a pressure terminal with a surface area of 1 cm². The musclehardness is estimated by recording the relation between the appliedpressure and the displacement of the skin over the muscle. Allcalculations are performed by a software-program in order to avoidobserver bias. Hardness is expressed in kPa/cm We have previouslydemonstrated that the hardness meter can measure muscle hardnessreliably if the same observer is used throughout a study (Ashina et al.1998b).

Pressure Pain Thresholds.

An electronic pressure algometer (Somedic AB, Stockholm, Sweden) wasused to measure pressure pain thresholds. The algometer has beendescribed in detail elsewhere (Jensen et al. 1986). A circularstimulation probe (0.50 cm²) and a pressure loading rate of 22 kPa/s (1kPa=10³ N/m²) were used.

Methods

The recordings were performed in a standardized manner by the sameobserver, a trained technician (HA) throughout the study. All parameterswere recorded at baseline, 60 and 120 minutes after start of infusion.The trial vas designed as a double blind, placebo controlled, crossoverstudy. The first part of the study examined the analgesic effect ofL-NMMA and has previously been described in detail (Ashina et al.1998a). Briefly patients were randomized to receive 6 m&/kg L-NMMA(Clinalfa, Switzerland) or placebo (isotonic glucose) over 15 minutesinto an antecubital vein on two days separated by at least one week. Thepatients were not allowed to take analgesics 12 hours prior to theexamination. Headache intensity was measured on a 100 mm Visual AnalogScale (VAS) (0—headache and 100—worst imaginable headache) before,during and after start of infusion.

Muscle Hardness.

The muscle hardness was measured at a standard anatomical a point on thetrapezius muscle on the non-dominant side, as previously described(Ashina et al. 1998b). Briefly, the point was located on the center ofthe descending part of the trapezius muscle midway between the processusspinosus of the seventh cervical vertebra and the acromion. The musclehardness was calculated as the mean of five consecutive determinations.All recordings were stored in the computer, and they were not analyzedbefore the study was completed.

Total Tenderness.

Tenderness of pericranial myofascial tissues vas recorded according tothe Total Tenderness Scoring system (Langemark and Olesen 1987), whichhas previously proved to be reliable (Bendtsen et al. 1995). Eight pairsof muscles and tendon insertions (masseter, temporal, frontal,stemocleidomastoid and trapezius muscles, coronoid and mastoidprocesses, and neck muscle insertions) were palpated. Tenderness wasscored on a 4-point (0-3) scale at each location (local tendernessscore) and values from left and right sides were summed to a TotalTenderness Score (TTS) (maximum possible score=48).

Pressure Pain Thresholds.

Pressure pain detection thresholds (PPDTs) were measured at the dorsumof the second finger (middle phalanx) and at a fixed point at theanterior part of the temporal muscle as previously described (Bendtsenet al. 1996b). Measurements were performed at the non-dominant side. ThePPDT was defined as the pressure at which the sensation changed frompressure alone to pain. The subject indicated that the pain thresholdwas reached by pressing a handheld button. The algometer display wasthereby Afrozen® and the pressure was immediately released. Eachthreshold was calculated as the mean of five consecutive determinationsperformed with intervals of approximately 30 seconds.

Data Analysis and Statistics

Results are presented as means SDs. For each of the variables, the sumof the differences between the pretreatment value and each of thepost-treatment values was calculated in order to obtain a summarymeasure of effect for each treatment (Matthews et al. 1990). The summaryscores calculated for active treatment and placebo were compared by useof die Wilcoxon Signed Ranks test Within each treatment pretreatmentvalues were compared with values at 60 and 120 minutes post dosing byuse of the Wilcoxon Signed Ranks test. Five percent was accepted aslevel of significance.

Results

Muscle hardness The summary scores of muscle hardness of the trapeziusmuscle was reduced significantly more following treatment with L-NMMAcompared with placebo (p=0.04) (FIG. 17). Compared to baseline, hardnesswas significantly reduced at 60 and 120 minutes after treatment withL-NM (p=0.04 and p<0.05, respectively). There was no significantreduction in muscle hardness at any time after treatment with placebo(Table XVIII).

Tenderness.

The summary of tenderness score tended to be reduced more followingtreatment with L-NMMA than with placebo, but the difference was notstatistically significant (p=0.11) (FIG. 18). However, compared tobaseline TTS was significantly reduced at 60 and 120 minutes aftertreatment with L-NMMA compared with pre-treatment values (p=0.007 andp=0.008, respectively). There was no significant reduction in TTS at anytime after treatment with placebo (Table XVIII).

Pressure Pain Thresholds.

There was no significant difference between PPDTs recorded duringtreatment with L-NMMA and placebo (finger: p=0.78 and temporal region:p=0.77). There were also no changes in PPDTs at 60 and 120 minutes aftertreatment with L-NMMA compared with pre-treatment values neither in thefinger nor in the temporal region (Table XVII). Compared to baselinePPDT decreased significantly in the finger (p=0.04), but not in thetemporal region following treatment with placebo (Table XVIII).

Pain Intensity.

Pain Intensity was significantly more reduced following treatment withL-NA than following treatment with placebo (FIG. 19) as previouslyreported (Ashina et al. 1998a). Pain scores were significantly reducedat each time point after treatment with L-NMMA, while there was nosignificant reduction in pain intensity at any time point aftertreatment with placebo (FIG. 19).

Discussion

In the present study, chronic tension-type headache was used as a modelfor chronic myofascial pain, since nociception from myofascial tissuesprobably plays an important role in the pathophysiology of chronictension-type headache. Thus, several studies have consistently reportedincreased myofascial tenderness as the most prominent abnormal findingin patients with chronic tension-type headache (Langemark and Olesen1987; Jensen et al. 1993; Jensen et al. 1998; Bendtsen et al. 1996b;Lipchik et al. 1997; Ashina et al. 1998b). A further support formyofascial involvement is the recent findings of increased musclehardness (Sakai et al. 1995) and a positive correlation between musclehardness and tenderness in chronic tension-type headache (Ashina et al.1998b). The mechanisms contributing to the increased tenderness andmuscle hardness are unknown. Recently it has been suggested that theincreased tenderness in patients with chronic tension-type headache andfibromyalgia may be due to central sensitization of spinal dorsal hornneurons induced by prolonged nociceptive input from myofascial tissues(Bendtsen et al. 1996a, 1997; Jensen et al. 1998). An investigation ofmyofascial tenderness and muscle hardness in patients with chronictension-type headache may therefore contribute to our understanding ofmyofascial pain.

Animal experiments have suggested that NO is an important transmitter inpain pathways of the spinal cord and that sensitization of thesepathways may be caused by or associated with activation of NOS and thegeneration of NO (Haley et al. 1992; Meller et al. 1992; Meller andGebhart 1993). In support for this, it has recently been shown in animalmodels of persistent pain that NOS inhibitors reduce spinal dorsal hornsensitization induced by continues painful input from the periphery(Meller et al. 1994; Roche et al. 1996; Mao et al. 1997). In addition,we have recently demonstrated that NOS inhibition has an analgesiceffect in patients with chronic myofascial pain (Ashina et al. 1998a).In the latter study we found that headache intensity was significantlyreduced during treatment with L-NMMA compared with placebo. The presentstudy provides important information about the mechanisms of theantinociceptive action of NOS inhibition in chronic myofascial pain. Wefound that both muscle hardness and tenderness were significantlyreduced at each time point after treatment with L-NMMA, while there wasno significant reduction in muscle hardness or tenderness at any timeafter treatment with placebo. Although the tenderness was significantlyreduced, the reduction of tenderness compared to placebo was notsignificant. This may be due to lack of statistical power. The musclehardness was significantly reduced following treatment with L-NMMAcompared to placebo. Although statistically significant, the reductionof hardness was very small. This is understandable because the increasedhardness is a rather stable feature (Ashina et al. 1998c) which is noteasy to change in an acute experiment. Similar arguments apply tomyofascial tenderness (Jensen et al. 1998). Long term treatment couldperhaps result in larger changes. The importance of the present resultslies in the proof of concept not in the magnitude of the effect Thepressure pain detection thresholds in the finger and temporal regionwere largely unchanged following treatment with L-NMMA. This indicatesthat L-NMMA did not significantly alter general pain sensitivity. Thequestions are what mechanisms leading to the increased muscle hardnessand tenderness; how L-NMMA modulates muscle hardness and tenderness; andwhether the effects of L-NMMA observed in the present study are due toan action in muscle or in the CNS? It has been shown that the centralneuroplastic changes may increase the drive to motor neurons both at thesupraspinal and the segmental level (Woolf 1983). In this way it ispossible that sustained muscle contraction due to increasedhypersensitivity in CNS contributes to increased muscle hardness andtenderness in chronic tension-type headache. This is supported by recentfindings of increased tenderness and muscle activity in patients withchronic tension-type headache was found not only on days with headachebut also on days without headache (Lipchik et al. 1997; Ashina et al.1998b; Jensen et al. 1998). Furthermore, muscle hardness recorded inpatients on days with headache did not differ from hardness recorded ondays without headache (Ashina et al. submitted 1998b). Collectively,these results indicate that permanently altered muscle hardness,tenderness and muscle activity may reflect an increased input frommyofascial nociceptors with subsequent sensitization of second orderneurons. L-NMMA inhibits all three types of NOS (endothelial NOS,neuronal NOS and inducible NOS) (Southan and Szabo 1996) and richsources of nNOS are present not only in nervous tissue but also in allstriated muscles of mammals (Grozdanovic et al. 1995). In addition tonNOS, skeletal muscles also contain nNOS. Recent study has demonstratedthat NO has important physiological functions in skeletal muscles suchas promoting relaxation and modulating increases in contraction (Kobziket al. 1994). Interestingly, contractile function of muscles wasenhanced by blockers of NO synthase (Kobzik et al. 1994). Because ofthis inverse correlation between contractile function and nNOS activity,one could expect that L-NMMA will induce the contraction of muscle withsubsequent increase of muscle hardness and tenderness. However, in thepresent study we observed the reduction of muscle hardness andtenderness following treatment with L-NMMA. Thus, the effects of L-NMMAobserved in the present study may be due to reduction of sensitizationof second order neurons receiving input from myofascial tissues andlocating at the level of the spinal dorsal horn/trigeminal nucleus.

The increased muscle hardness and tenderness may reflect a tissue oedemaor metabolic alterations due to microcirculatory disturbance (Henrikssonet al. 1993). It is possible that L-NMMA acts directly in myofascialtissues or nociceptors located in such tissues. Thus, the ability of NOSinhibitors to cause vasoconstriction (Rees et al. 1990) may preventinflammatory mediators and algogenic substances involved in hardness andtenderness from reaching their site of action (Haley et al. 1992). Inaddition, it has been demonstrated that NOS inhibitors haveantinociceptive effect after peripheral administration (Haley et al.1992; Kindgren-Milles and Arndt 1996; Nakamura et al. 1996). However,the exact role of NO in the periphery is still far from understood, andadditional research is needed to clarify whether NO may activate orsensitize peripheral nociceptors. The antinociceptive effect of NOSinhibition might also result from non-specific effects elicited byL-NMMA, such as changes in blood pressure and pulse rate. Mean arterialblood pressure and pulse rate were continuously monitored in the presentstudy. We found that the peak increase in mean arterial blood pressure(12%) and maximum decrease in pulse rate (16%) occurred 15 and 10minutes respectively after treatment with L-NMMA. The difference in themean arterial blood pressure and pulse rate between L-NMMA and placebodisappeared 60 minutes after start of infusion (Ashina et al. 1998a). Incontrast, the antinociceptive effect on headache intensity and thereduction of muscle hardness and tenderness lasted at least 120 minutesafter start of infusion. It therefore seems unlikely that the observedeffects of L-NMMA were caused by hypertensive effects of the agent Inconclusion, the present study indicates that the NOS inhibitor L-NMMAelicits its antinociceptive effect in myofascial pain by modulation ofnociceptive information from myofascial tissues. This antinociceptiveeffect is probably caused by reduction of central sensitization at thelevel of the spinal dorsal horn/trigeminal nucleus.

TABLE XVII Clinical data on patients. Patients Number 16 Females/males12/4 Age, years 39(23-52) Headache frequency, days/4 weeks 22(15-28)Mean values with range given within parentheses.

TABLE XVIII Muscle hardness, Total Tenderness Score (TTS) and pressurepain detection thresholds (PPDT) in the finger and the temporal region(TR) recorded before and 60 and 120 minutes after start of the infusionof L-NMMA or placebo. Baseline 60 minutes 120 minutes Muscle hardnessL-NMMA 107 ″ 17 101 ″ 17* 101 ″ 17* Placebo 106 ″ 18 104 ″ 17^(NS) 105 ″22^(NS) TTS L-NMMA  18 ″ 11  15 ″ 11**  14 ″ 11** Placebo  17 ″ 12  16 ″13^(NS)  15 ″ 13^(NS) PPDT/finger L-NMMA 455 ″ 155 436 ″ 129^(NS) 449 ″144^(NS) Placebo 457 ″ 141 435 ″ 143^(NS) 420 ″ 130* PPDT/TR L-NMMA 279″ 108 264 ″ 86^(NS) 277 ″ 95^(NS) Placebo 274 ″ 104 271 ″ 109^(NS) 262 ″95^(NS) Mean values ( ″ SDs) are given. Post treatment values comparedwith pre-treatment values (Wilcoxon Signed Ranks test). ** = p <0.009, * = p < 0.05 and NS = not significant.

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What is claimed is:
 1. A method for treatment or prevention oftension-type headache in a person in need of such treatment, comprisingadministering to said person an amount of an agent effective to interactwith neuronal transmission connected with pain perception, so as toprevent or reduce central sensitization, wherein said agent is an agentwhich, in the peripheral and/or central nervous system, is capable ofsubstantially inhibiting the production of nitric oxide or substantiallycounteracting the action of nitric oxide or substantially inhibiting theproduction of nitric oxide synthase (NOS) or substantially counteractingthe action of nitric oxide synthase (NOS), with the proviso that saidinteraction is not performed by administering ethyl2-amino-6-(4-fluorobeznylamino)-3-pyridylcarbamate or an arylglycinamidederivative as defined herein.
 2. A method according to claim 1, whereinthe agent comprises a nitric oxide inhibitor.
 3. A method according toclaim 2, wherein the agent comprises an NOS inhibitor.
 4. A methodaccording to claim 3, wherein the agent is selected from the groupconsisting of arginine derivatives, citrulline derivatives, indazoles,imidazolin-N-oxides, phenylimidazoles, 21-aminosteroids, biphenyls,piperidine derivatives or derivatives of any of the above which are NOSinhibitors or prodrugs thereof.
 5. The method of claim 3 in which theagent is an arginine derivative.
 6. The method of claim 3 in which theagent is L-NMMA.
 7. The method of claim 3 in which the agent is selectedfrom the group consisting of L-NAME, L-NMMA, L-NIO, L-NNA, anddimethyl-L-arginine.
 8. A method for treatment or prevention oftension-type headache in a person in need of such treatment, comprisingadministering to said person an amount of an agent which, in theperipheral and/or central nervous system, is effective to specificallyinteract with neuronal transmission connected with pain perception bysubstantially antagonizing the action of nitric oxide or nitric oxidesynthase (NOS).
 9. A method according to claim 8, wherein the agentcomprises a nitric oxide inhibitor.
 10. A method according to claim 8,wherein the agent comprises an NOS inhibitor.
 11. A method of treatmentof tension-type headache comprising administering to a person in need ofsuch treatment an effective amount of an agent which is capable ofsubstantially inhibiting the action of the enzyme nitric oxide synthase(NOS) and thereby reduces chronic pain in connection with tension-typeheadache.
 12. A method according to claim 11, wherein the agent isselected from the group consisting of arginine derivatives, citrullinederivatives, indazoles, imidazolin-N-oxides, phenylimidazoles,biphenyls, piperidine derivatives or derivatives of any of the abovewhich are NOS inhibitors or prodrugs thereof.